U.S. Fish & Wildlife Service
Status and Trends of
Wetlands in the Conterminous
United States 1998 to 2004
Inside front cover
Status and Trends of
Wetlands in the Conterminous
United States 1998 to 2004
T. E. Dahl
U.S. Fish and Wildlife Service
Fisheries and Habitat Conservation
Washington, D.C.
Opposite page: Louisiana, 2005.
Previous, title page: Freshwater wetland
in the southeast U.S., 2005.
Acknowledgments
Many agencies, organizations,
and individuals contributed their
time, energy, and expertise to the
completion of this report. The author
would like to specifically recognize
the following individuals for their
contributions. From the Fish and
Wildlife Service:
Dr. Benjamin Tuggle, John Cooper,
Herb Bergquist, Jim Dick, Jonathan
Hall , Bill Pearson, Becky Stanley ,
Dr. Mamie Parker, Everett Wilson,
Jill Parker, Robin Nims Elliott.
From the U.S. Geological Survey:
Greg Allord, Dave McCulloch, Mitch
Bergeson, Jane Harner,
Liz Ciganovich, Marta Anderson,
Dick Vraga, Tim Saultz, Mike
Duncan, Ron Keeler and the
staff of the Advanced Systems
Center. From the National Park
Service–Cumberland Island
National Seashore: Ginger Cox,
Ron Crawford and George Lewis.
From the Interagency Field Team:
Sally Benjamin, USDA–Farm
Services Agency; Patricia Delgado,
NOAA, National Marine Fisheries
Service; Dr. Jeff Goebel and Daryl
Lund, USDA–Natural Resources
Conservation Service; David Olsen,
U.S. Army Corps of Engineers; and
Myra Price, U.S. Environmental
Protection Agency.
Peer review of the manuscript was
provided by the following technical
experts: Ms. Peg Bostwick, Michigan
Dept. of Environmental Quality,
Lansing, MI; Dr. Ken Burham,
Statistician, Department of Fishery
and Wildlife Biology, Colorado State
University, Fort Collins, CO; Mr.
Retired.
Current affiliation: NOAA, National Marine
Fisheries Service.
Marvin Hubbell, U.S. Army Corps of
Engineers, Rock Island, IL;
Mr. William Knapp, Deputy Science
Advisor, U.S. Fish and Wildlife
Service, Arlington, VA; Ms. Janet
Morlan, Oregon Dept. of State Lands,
Salem, OR; Dr. N. Scott Urquhart
Research Scientist, Department of
Statistics, Colorado State University,
Fort Collins, CO; Mr. Joel Wagner,
Hydrologist, National Park Service,
Denver, CO; Dr. Dennis Whigham,
Senior Scientist, Smithsonian
Environmental Research Center,
Edgewater, MD; Dr. Joy Zedler,
Professor of Botany and Aldo
Leopold Chair in Restoration
Ecology, University of Wisconsin,
Madison, WI.
This report is the culmination
of technical collaboration and
partnerships. A more complete listing
of some of the cooperators appears at
the end of this report.
Publication design and layout of the
report were done by the Cartography
and Publishing Program, U.S.
Geological Survey, Madison,
Wisconsin.
Photographs are by Thomas Dahl
unless otherwise noted.
This report should be cited as follows:
Dahl, T.E. 2006. Status and trends
of wetlands in the conterminous
United States 1998 to 2004.
U.S. Department of the Interior;
Fish and Wildlife Service,
Washington, D.C. 112 pp.
Tundra swans (Cygnus columbianus) and other waterfowl congregate in the freshwater marshes along
the upper Mississippi River. Photo courtesy of FWS.
Funding for this study was
provided by the following
agencies:
Environmental Protection Agency
Department of Agriculture
Farm Services Administration
Natural Resources Conservation Service
Department of Commerce
National Marine Fisheries Service
Department of the Army
Army Corps of Engineers
Department of Interior
Fish and Wildlife Service
The Council of Environmental Quality has
coordinated these interagency efforts.
A freshwater emergent wetland in Nebraska, 2005.
Preface
Secretary, Department of the Interior
On Earth Day 2004, President Bush
unveiled a new policy for our nation’s
wetlands. Moving beyond “no net
loss” of wetlands, the President
challenged the nation to increase the
quantity as well as quality of these
important resources, and set a goal
of restoring, improving and
protecting more than 3 million
acres in five years.
The President recognized that a
continuous effort to track progress
toward achieving the various aspects
of the Administration’s new policies
would be important. The Fish and
Wildlife Service was in a unique
position to provide the nation with
sound scientific information
assessing trends in the quantity of
wetland gains and losses. As part of
that same 2004 Earth Day message,
the President directed the Service
to accelerate the completion of this
study and report the results.
This is the Administration’s report
to Congress that provides the nation
with scientific and statistical results
on progress made toward our
national wetlands acreage goals.
I am pleased to report that the
nation is making excellent progress
in meeting these wetland goals. For
the first time net wetland gains,
achieved through the contributions
of restoration and creation activities,
surpassed net wetland losses.
This is the result of a multitude of
governmental, corporate and private
partnerships working together to
secure and conserve our wetland
resources for future generations.
This report does not draw
conclusions regarding trends in
the quality of the nation’s wetlands.
The Status and Trends Study collects
data on wetland acreage gains and
losses, as it has for the past 50 years.
However, it is timely to examine
the quality, function, and condition
of such wetland acreage. Such an
examination will be undertaken
by agencies participating in the
President’s Wetlands Initiative.
U.S. Customary to Metric
inches (in.) x 25.40 = millimeters (mm)
inches (in.) x 2.54 = centimeters (cm)
feet (ft) x 0.30 = meters (m)
miles (mi) x 1.61 = kilometers (km)
nautical miles (nmi) x 1.85 = kilometers (km)
square feet (ft2) x 0.09 = square meters (m2)
square miles (mi2) x 2.59 = square kilometers (km2)
acres (A) x 0.40 = hectares (ha)
Fahrenheit degrees (F) → 0.56 (F - 32) = Celsius degrees (C)
Metric to U.S. Customary
millimeters (mm) x 0.04 = inches (in.)
centimeters (cm) x 0.39 = feet (ft)
meters (m) x 3.28 = feet (ft)
kilometers (km) x 0.62 = miles (mi)
square meters (m2) x 10.76 = square feet (ft2)
square kilometers (km2) x 0.39 = square miles (mi2)
hectares (ha) x 2.47 = acres (A)
Celsius degrees (C) → 1.8 (C) + 32) = Fahrenheit degrees (F)
General Disclaimer
Conversion Table
The use of trade, product, industry or firm names or products in this report is for informative
purposes only and does not constitute an endorsement by the U.S. Government or the Fish and
Wildlife Service.
Contents
Preface......................................................................................................................................................................... 7
Executive Summary.................................................................................................................................................15
Introduction.............................................................................................................................................................. 19
Study Design and Procedures................................................................................................................................21
Study Objectives................................................................................................................................................21
Sampling Design................................................................................................................................................ 24
Types and Dates of Imagery............................................................................................................................26
Technological Advances....................................................................................................................................30
Methods of Data Collection and Image Analysis...........................................................................................30
Wetland Change Detection............................................................................................................................... 31
Field Verification................................................................................................................................................ 3
Quality Control................................................................................................................................................... 34
Statistical Analysis............................................................................................................................................36
Limitations.......................................................................................................................................................... 37
Attribution of Wetland Losses.........................................................................................................................39
Results and Discussion............................................................................................................................................43
Status of the Nation’s Wetlands.......................................................................................................................43
Attribution of Wetland Gain and Loss.............................................................................................................47
Intertidal Estuarine and Marine Wetland Resources...................................................................................48
Marine and Estuarine Beaches, Tidal Bars, Flats and Shoals.....................................................................50
Estuarine Emergent Wetlands........................................................................................................................52
Estuarine Shrub Wetlands...............................................................................................................................5
Wetland Values for Fish and Wildlife–insert–Wetlands and Fish...............................................................57
Freshwater Wetland Resources.......................................................................................................................61
Freshwater Lakes and Reservoirs...................................................................................................................78
Terminology and Tracking Wetland Gains......................................................................................................78
Wetland Restoration and Creation on Conservation Lands................................................................................81
Wetland Restoration–insert–Restoration on the Upper Mississippi River.........................................82
Wetland Restoration–insert–Restoring Iowa’s Prairie Marshes..........................................................85
Monitoring Wetland Quantity and Quality­—
Beyond No-Net-Loss............................................................89
Minnesota’s Comprehensive Wetland Assessment and Monitoring Strategy....................................90
Summary................................................................................................................................................................... 93
References Cited...................................................................................................................................................... 95
Acknowledgement of Cooperators.........................................................................................................................98
Appendix A: Definitoins of habitat categories used in this study.....................................................................101
Appendix B: Hammond (1970) physiographic regions of the United States...................................................105
Appendix C: Wetland change from 1998 to 2004.................................................................................................106
Appendix D: Representative Wetland Restoration Programs and Activities.................................................109
10
List of Figures
Figure 1. A cypress (Taxodium distichum) wetland near the White River, Arkansas, 2005.........................19
Figure 2. A gallery of wetland images....................................................................................................................20
Figure 3. Open water lakes, such as this reservoir were classified as deepwater habitats
if they exceeded 20 acres (8 ha). Piney Run Lake, Maryland, 2005...................................................................2
Figure 4. Coastal wetlands offshore from the mainland include salt marsh
(estuarine emergent) (A), shoals (B), tidal flats (C) and bars.............................................................................24
Figure 5. Physiographic subdivisions of North Carolina and sample plot distribution as used
in this study...............................................................................................................................................................25
Figure 6. High resolution, infrared Ikonos satellite image of bogs (A), lakes (B) and wetlands (C)
of northern Wisconsin, spring 2005........................................................................................................................26
Figure 7. Early spring 2005 Ikonos satellite image of Michigan. Leaf-off condition
made recognition of wetland features easier.........................................................................................................27
Figure 8. Mean date of imagery used by state......................................................................................................28
Figure 9. True color NAIP photographs scale show farmland (A), forest (B), wetlands (C)
and lakes (D) in Indiana, 2003................................................................................................................................29
Figure 10. A small wetland basin estimated to have been about seven square meters...................................30
Figure 1. Change detection involved a comparison of plots at two different times (T1 and T2)..................31
Figure 12. A true color aerial photograph shows a new drainage network
(indicated by red arrow) and provides visual evidence of wetland loss.............................................................32
Figure 13. Lands in transition from one land use category to another pose unique challenges
for image analysts....................................................................................................................................................32
Figure 14. Field verification was completed at sites in the 35 states as shown on the map............................3
Figure 15. Topographic maps in digital raster graphics format were used as auxillary
information and for quality control........................................................................................................................35
Figure 16. Digital wetlands status and trends data were viewed combined with contemporary
georeferenced color infrared imagery of the study areas....................................................................................35
Figure 17. The Pacific coastline..............................................................................................................................37
Figure 18 A and B. Commercial rice fields where water was pumped to flood the rice crop.........................38
Figure 19 A and B. Examples of agricultural land use........................................................................................39
Figure 20. Trees planted in rows with uniform crown height (A) and block clear cuts [blue-green
feature in center (B)] were indicators of managed forest plantations..............................................................40
Figure 21. Urban wetlands (shown as dark blue-black) outside of a shopping mall are
surrounded by high density urban development. New Jersey, 2003, color infrared photograph...................41
Figure 2. Wetland area compared to the total land area of the conterminous United States, 2004............43
Figure 23. Salt marsh along the Ecofina River, Florida .....................................................................................45
Figure 24. Percentage of estimated estuarine and freshwater wetland area and covertypes, 2004..............45
Figure 25. A freshwater wetland in the southeastern United States 2005........................................................46
Figure 26. Average annual net loss and gain estimates for the conterminous
United States, 1954 to 2004.....................................................................................................................................46
11
Figure 27. Wetlands gained or lost from upland categories and deepwater, 1998 to 2004..............................47
Figure 28. Composition of marine and estuarine intertidal wetlands, 2004......................................................48
Figure 29. Estimated percent loss of intertidal estuarine and marine wetlands to
deepwater and development, 1998 to 2004.............................................................................................................49
Figure 30. Non-vegetated tidal flats grade into sparsely vegetated beach ridges. These areas
are important for a variety of birds, sea turtles and other marine life..............................................................50
Figure 31. Intertidal marine beaches provide important habitat for shorebirds.............................................51
Figure 32. The black necked stilt (Himantopus mexicanus) inhabits mud flats, pools,
back water beaches and brackish ponds of saltwater marshes among other wetland habitats......................51
Figure 3. New shoals and sand bars are continually forming in shallow water areas.
This image shows a new feature (brightest white areas) off the coast of Virginia, 2004.................................51
Figure 34. High altitude infrared photograph of salt marsh (darker mottles), coastal Georgia, 2004..........52
Figure 35. Estuarine emergent losses as observed in this study along the Atlantic and Gulf of Mexico.
Inset shows close up of Louisiana where most losses occurred between 1998 and 2004.................................53
Figure 36. Pelican Island, Florida, the nation’s first National Wildlife Refuge is located in
the Indian River Lagoon, a biologically diverse estuary of mangrove islands, salt marsh,
and maritime hammocks.........................................................................................................................................5
Figure 37 A–C. Long-term trends in A) all intertidal wetlands, B) estuarine vegetated wetlands and
C) estuarine non-vegetated wetlands, 1950s to 2004............................................................................................56
Figure 38. Approximate density and distribution of freshwater wetland acreage gains indentified
in the samples of this study.....................................................................................................................................62
Figure 39. A tile drained wetland basin has been restored. Ohio, 2005.............................................................62
Figure 40. Wetland restoration (freshwater emergent) on land previously classified
as upland “other.”.....................................................................................................................................................63
Figure 41. Wetland restoration attributed to agricultural conservation programs in the
upper midwest, 2004................................................................................................................................................64
Figure 42. A restored wetland basin.......................................................................................................................65
Figure 43 A and B. Private efforts to restore wetlands also contributed to the national acreage
base in this study. A) western Minnesota, 2004; B) Stone Lake,
Wisconsin, 2005.........................................................................................................................................................65
Figure 4. Example of wetland loss. Fill being placed into a wetland pond in Ohio, 2005..............................6
Figure 45. An emergent wetland in rural Pennsylvania, 2005, in the process of being filled.
Both examples in Figures 46 and 47 were attributed to Rural Development...................................................6
Figure 46. Areas experiencing wetland loss due to development, 1998 to 2004...............................................67
Figure 47. Development in rapidly growing area of south Florida....................................................................68
Figure 48. Trends in the estimated annual loss rate of freshwater vegetated
wetland area, 1974 to 2004......................................................................................................................................69
Figure 49. A mitigation banking site. As wetlands were converted elsewhere, cells of the
mitigation bank were flooded to create replacement wetland. 2004..................................................................69
Figure 50. Estimated percent loss of forested wetlands to the various upland land use
categories between 1998 and 2004..........................................................................................................................70
Figure 51. Forested wetland. Alabama, 2005. Photo courtesy of South Dakota State University.................70
Figure 52. A freshwater wetland dominated by the woody shrub False Indigo (Amorpha fruticosa).........71
Figure 53. Long-term trends in freshwater forested and shrub wetlands, 1950s to 2004..............................71
Opposite page: Freshwater wetlands of the Yosemite Valley, California.
12
Figure 54. This field has been squared off by agricultural drainage (surface ditch indicated
with red arrow). New Jersey, 2003..........................................................................................................................72
Figure 5. Subtle wetland drainage practices in the prairie pothole region of South Dakota........................73
Figure 56. Long-term trends in freshwater emergent wetlands, 1954 to 2004................................................73
Figure 57. A freshwater pond in central Kansas is starting to support emergent vegetation, 2005.............74
Figure 58. Number and approximate location of new freshwater ponds
created between 1998 and 2004..............................................................................................................................75
Figure 59. A newly created open water pond as part of a golf course. Maryland, 2005..................................75
Figure 62 A–D. Different ponds have been constructed for different purposes throughout
the United States......................................................................................................................................................76
Figure 61. Color infrared aerial photograph of new development in south Florida. Ponds and small
residential lakes (shown as dark blue) are surrounded by new housing...........................................................7
Figure 62. Commercial cranberry operations had created several
open water ponds (dark blue areas)........................................................................................................................7
Figure 63. Long-term trends in freshwater pond acreage, 1954 to 2004...........................................................7
Figure 64A and B. Freshwater lakes provide wildlife and fish habitat as well as opportunities for
recreation and education.........................................................................................................................................78
Figure 65. Created wetland on an area that was upland (dry land)...................................................................79
Figure 6. A wetland restoration (reestablishment). This former wetland basin had been completely
drained and reclassified as upland.........................................................................................................................79
Figure 67. “Improved” wetland or wetland enhancement—hydrology has been restored to
an existing albeit degraded wetland.......................................................................................................................79
Figure 68 . Wetland protection or preservation—included pre-existing wetland acres either
owned or leased long-term by a federal agency....................................................................................................79
Figure 69. A system of federal lands including National Wildlife Refuges and
Wetland Management Districts are restoring and enhancing wetland acres...................................................81
Table 1. Wetland, deepwater, and upland categories used to conduct
wetland status and trends studies..........................................................................................................................23
Table 2. Change in wetland area for selected wetland and deepwater categories, 1998 to 2004 ...................4
Table 3. Changes to estuarine and marine wetlands, 1998 to 2004.....................................................................49
Table 4. Contrasting different estimates of wetland loss in Louisiana..............................................................54
Table 5. Changes in freshwater wetland area between 1998 and 2004..............................................................61
Table 6. Contrasting the Fish and Wildlife Service’s Wetlands Status and Trends with the Council on
Environmental Quality report (2005) on federal efforts to track wetland gains..............................................80
List of Tables
13
14
Executive Summary
The first statistical wetlands status
and trends report (Frayer et al.
1983) estimated the rate of wetland
loss between the mid 1950s and the
mid 1970s at 458,000 acres (185,400
ha) per year. There have been
dramatic changes since that era
when wetlands were largely thought
of as a hindrance to development.
The first indications of those
changes came from the Fish and
Wildlife Service’s updated status
and trends report (Dahl and Johnson
1991) covering the mid 1970s to the
mid 1980s. The estimated rate of
wetland loss had declined to 290,000
acres (117,400 ha) per year.
In 2000, the Fish and Wildlife
Service produced the third
national status and trends report
documenting changes that occurred
between 1986 and 1997. Findings
from that report indicated the
annual loss rate was 58,500 acres
(23,700 ha), an eighty percent
reduction in the average annual rate
of wetland loss.
On Earth Day 2004, President Bush
announced a wetlands initiative that
established a federal policy beyond
“no net loss” of wetlands. The policy
seeks to attain an overall increase
in the quality and quantity of
wetlands. The President set a goal of
restoring, improving and protecting
more than 3 million acres (1.2
million ha) in five years. To continue
tracking wetland acreage trends, the
President further directed the Fish
and Wildlife Service to complete
an updated wetlands status and
trends study in 2005. This latest
report provides the nation with
scientific and statistical results on
the progress that has been made
toward achieving national wetland
quantity goals. This report does not
assess the quality or condition of
the nation’s wetlands. The Status
and Trends Study collects data on
wetland acreage gains and losses,
For over half a century the Fish
and Wildlife Service has been
monitoring wetland trends of the
nation. In 1956, the first report on
wetland status and classification
provided indications that wetland
habitat for migratory waterfowl had
experienced substantial declines
(Shaw and Fredine 1956).
Over the intervening 51 years,
the Fish and Wildlife Service has
implemented a scientifically based
process to periodically measure
wetland status and trends in the
conterminous United States. The
Fish and Wildlife Service’s Wetlands
Status and Trends study was
developed specifically for monitoring
the nation’s wetland area using a
single, consistent definition and
study protocol. The Fish and Wildlife
Service has specialized knowledge
of wetland habitats, classification,
and ecological changes and has used
that capability to conduct a series
of wetland monitoring studies that
document the status and trends of
our nation’s wetlands. This report is
the latest in that series of scientific
studies.
Data collected for the 1998 to 2004
Status and Trends Report has led to
the conclusion that for the first time
net wetland gains, acquired through
the contributions of restoration and
creation activities, surpassed net
wetland losses. There was a net gain
of 191,750 wetland acres (77,630
ha) nationwide which equates to an
average annual net gain of 32,000
acres (12,900 ha).
The efforts to monitor wetland
status and trends that are described
in this report have been enhanced
by the multi-agency involvement in
the study’s design, data collection,
verification, and peer review of the
findings. Interagency funding was
essential to the successful and timely
completion of the study.
A freshwater forested wetland of the
Great Lakes region, 2005.
15
as it has for the past 50 years.
However, it is timely to examine
the quality, function, and condition
of such wetland acreage. Such an
examination will be undertaken
by agencies participating in the
President’s Wetlands Initiative.
This study measured wetland
trends in the conterminous United
States between 1998 and 2004. The
estimates of estuarine emergent
area were made prior to Hurricanes
Katrina and Rita during the summer
of 2005. The Cowardin et al. (1979)
wetland definition was used to
describe wetland types. By design,
intertidal wetlands of the Pacific
coast, reefs and submerged aquatic
vegetation were excluded from this
study.
An interagency group of statisticians
developed the design for the national
status and trends study. The study
design consisted of 4,682 randomly
selected sample plots. Each plot is
four square miles (2,560 acres or
1,040 ha) in area. These plots were
examined, with the use of recent
remotely sensed data in combination
with field work, to determine
wetland change. Field verification
was completed for 1,504 (32 percent)
of the sample plots distributed in 35
states. Representatives from four
states and seven federal agencies
participated in field reconnaissance
trips.
Estimates were made of wetland
area by wetland type and changes
over time.
National Status
and Trends
This study found that there were
an estimated 107.7 million acres
(43.6 million ha) of wetlands in the
conterminous United States in 2004.
Ninety-five percent of the wetlands
were freshwater wetlands and five
percent were estuarine or marine
wetlands.
In the estuarine system, estuarine
emergents dominated, making up
an estimated 73 percent (almost 3.9
million acres or 1.6 million ha) of
all estuarine and marine wetlands.
Estuarine shrub wetlands made
up 13 percent of the area and non-vegetated
saltwater wetlands 14
percent.
In the freshwater system, forested
wetlands made up 51 percent of
the total area, the single largest
freshwater category. Freshwater
emergents made up an estimated
25.5 percent of the total area, shrub
wetlands 17 percent and freshwater
ponds 6.5 percent.
Wetland area increased by an
average 32,000 acres (12,900
ha.) annually. The net gain in
wetland area was attributed to
wetlands created, enhanced or
restored through regulatory
and nonregulatory restoration
programs. These gains in wetland
area occurred on active agricultural
lands, inactive agricultural lands,
and other lands. Freshwater wetland
losses to silviculture, urban and
rural development offset some
gains. Urban and rural development
combined accounted for an
estimated 61 percent of the net
freshwater wetlands lost between
1998 and 2004. This study reports
on changes in wetland acreage and
does not provide an assessment of
wetland functions or quality.
Intertidal
Estuarine and
Marine Wetland
Resources
Three major categories of estuarine
and marine wetlands were included
in this study: estuarine intertidal
emergents (salt and brackish water
marshes), estuarine shrub wetlands
(mangrove swamps) and estuarine
and marine intertidal non-vegetated
wetlands. This latter category
included exposed coastal beaches
subject to tidal flooding, shallow
water sand bars, tidal flats, tidally
exposed shoals, and sand spits.
In 2004, it was estimated there
were slightly more than 5.3
million acres (2.15 million ha) of
marine and estuarine wetlands in
the conterminous United States.
Estuarine emergent wetlands
declined by 0.9 percent. The average
annual rate of estuarine emergent
loss was 5,540 acres (2,240 ha). This
rate of loss was consistent with the
rate of salt marsh loss recorded from
1986 to 1997. Most of the losses of
estuarine emergent wetland were
due to loss to deep salt water and
occurred in coastal Louisiana. One
or more of several interrelated
factors may have contributed to
these losses including: deficiencies
in sediment deposition, canals and
artificially created waterways,
wave erosion, land subsidence, and
salt water intrusion causing marsh
disintegration.
There were an estimated 728,540
acres (294,960 ha) of intertidal
non-vegetated wetlands in 2004.
From 1998 to 2004 marine intertidal
beaches declined by 1,870 acres
(760 ha). Intertidal non-vegetated
wetland changes to urban and other
forms of upland development were
statistically insignificant in this
study.
There were an estimated 682,200
acres (276,190 ha) of estuarine shrub
wetland in 2004. This estimate
represented a small gain of about 800
acres (320 ha). The area of estuarine
shrub wetlands has been steady over
the past two decades.
Freshwater
Wetland
Resources
Large shifts between the freshwater
wetland types and uplands took
place between 1998 and 2004.
Freshwater wetland gains resulted
from restorations and the creation of
numerous freshwater ponds.
Agricultural conservation programs
were responsible for most of
the gross wetland restoration.
These gains came from lands in
“agriculture” category as well
as from conservation lands in
16
the “other” land use category.
Agricultural programs that
promoted pond construction
also contributed to the increased
freshwater pond acreage.
Ponds were included as freshwater
wetlands consistent with the
Cowardin et al. definition.
Freshwater pond acreage increased
by almost 700,000 acres (281,500 ha)
from 1998 to 2004, a 12.6 percent
increase in area. This was the
largest percent increase in area,
of any wetland type in this study.
Without the increased pond acreage,
wetland gains would not have
surpassed wetland losses during the
timeframe of this study. The creation
of artificial freshwater ponds has
played a major role in achieving
wetland quantity objectives.
The replacement of vegetated
wetland areas with ponds represents
a change in wetland classification.
Some freshwater ponds would not be
expected to provide the same range
of wetland values and functions as a
vegetated freshwater wetland.
Freshwater forested wetlands
were affected by two processes,
the conversion of forested wetland
to and from other wetland types
through cutting or the maturation of
trees, and loss of forested wetland
where wetland hydrology was
destroyed. Estimates indicated
that the area of freshwater forested
wetland increased. Between 1998
and 2004, forested wetland area
increased by an estimated 548,200
acres (221,950 ha). Most of these
changes came from small trees,
previously classified as wetland
shrubs, maturing and being re-classified
as forest.
Despite the net gains realized from
restoration and creation projects,
human induced wetland losses
continued to affect the trends of
freshwater vegetated wetlands—
especially freshwater emergent
marshes which declined by an
estimated 142,570 acres (57,720
ha). These wetlands are important
to a number of wildlife species.
Contributed inserts to the report
highlight the importance of wetlands
to fish and wildlife.
American avocets (Recurvirostra americana) at Bear River, Migratory Bird Refuge, Utah, a river delta wetland that attracts
hundreds of species of waterfowl and shorebirds. Photo courtesy of the FWS.
17
18
Introduction The mission of the Fish and Wildlife
Service is to conserve, protect, and
enhance fish, wildlife, plants, and
their habitats for the continuing
benefit of the American people. The
Fish and Wildlife Service supports
programs relating to migratory
birds, endangered species, certain
marine mammals, inland sport
fisheries and a system of 545
national wildlife refuges. The Fish
and Wildlife Service communicates
information essential for public
awareness and understanding
of the importance of fish and
wildlife resources and changes in
environmental conditions that can
affect the welfare of Americans.
To this end, the Fish and Wildlife
Service maintains an active role in
monitoring wetland habitats of the
nation.
The importance of wetlands as fish
and wildlife habitat has always been
the primary focus of the Fish and
Wildlife Service’s wetland activities.
Wetlands are transitional from truly
aquatic habitats to upland and as a
result, wetland abundance, type and
quality are directly reflected in the
health and abundance of many fish
and wildlife species.
The Emergency Wetlands Resources
Act (Public Law 99-645) requires
the Fish and Wildlife Service to
produce national wetlands status
and trend reports for the Congress
at ten year intervals. The Fish and
Wildlife Service has responded to
this mandate with national wetlands
status and trends reports in 1983,
1991 and 2000 (Frayer et al. 1983;
Tiner 1984; Dahl and Johnson 1991;
and Dahl 2000).
These wetland status and trend
reports have been used by federal,
state, local and tribal governments
to develop wetland conservation
strategies, measure the efficacy
of existing policies, and validate
comprehensive performance
toward halting loss and regaining
wetlands. Industry, the scientific
community, conservation groups,
decision makers and the public value
this contemporary information for
planning, decision-making, and on-the-
ground management.
Our nation’s wetlands goals have
historically been based on wetland
acreage and the ability to provide a
quantitative measure of the extent
of wetland area as a means to
measure progress toward achieving
the national goal of “no net loss.”
This concept was first formulated
as a national goal by the National
Wetlands Policy Forum (The
Conservation Foundation 1988)
and was later adopted as federal
policy by President George H.W.
Bush. In an effort to monitor the
status and trends in the quantity
and type of our nation’s wetlands, a
series of Fish and Wildlife Service
reports have documented a steadily
declining wetland loss rate. From
the mid 1950s to the mid 1970s, the
nation lost about 458,000 wetland
acres annually. This rate of loss
was substantially reduced to about
59,000 acres annually by 1997.
On Earth Day 2004, President
George W. Bush announced a
wetlands initiative that established a
federal policy beyond “no net loss” of
wetlands. The policy seeks to attain
an overall increase in the quality
and quantity of wetlands and set
a goal of restoring, improving and
protecting more than 3 million acres
(1.2 million ha) in five years (Council
on Environmental Quality 2005). To
continue tracking wetland trends,
the President further directed
the Fish and Wildlife Service to
complete an updated wetlands status
and trends study in 2005—five years
ahead of the mandated legislative
schedule.
This updated report used the
latest technologies in remote
sensing, geospatial analysis and
computerized mapping. The most
recent aerial and satellite imagery
available was analyzed to document
wetland change on 4,682 two-mile
square (5.2 sq. km) sample plots
located throughout the 48 states. It
covers the period from 1998 to 2004,
and provides the most recent and
comprehensive quantitative measure
of the areal extent of all wetlands
in the conterminous United States
regardless of ownership. The study
provides no qualitative assessments
of wetland functions.
Figure 1. A cypress (Taxodium
distichum) wetland near the White
River, Arkansas, 2005.
19
20
Study Objectives
This study was designed to provide
the nation with current, scientifically
valid information on the status
and extent of wetland resources
regardless of ownership and to
measure change in those resources
over time.
Wetland Definition and Classification
The Fish and Wildlife Service
used the Cowardin et al. (1979)
definition of wetland. This definition
is the standard for the agency
and is the national standard for
wetland mapping, monitoring
and data reporting as determined
by the Federal Geographic Data
Committee. It is a two-part
definition as indicated below:
Ephemeral waters, which are not
recognized as a wetland type, and
certain types of “farmed wetlands”
as defined by the Food Security
Act were not included in this
study because they do not meet
the Cowardin et al. definition.
The definition and classification of
wetland types have been consistent
in every status and trends study
conducted by the Fish and Wildlife
Service. Habitat category definitions
are given in synoptic form in Table
1. The reader is encouraged to also
review Appendix A, which provides
complete definitions of wetland
types and land use categories used
in this study.
Wetlands are lands transitional between terrestrial and aquatic
systems where the water table is usually at or near the surface
or the land is covered by shallow water.
For purposes of this classification wetlands must have one or
more of the following three attributes: (1) at least periodically,
the land supports predominantly hydrophytes, (2) the substrate
is predominantly undrained hydric soil, and (3) the substrate is
nonsoil and is saturated with water or covered by shallow water
at some time during the growing season of each year.
Study Design and Procedures
Figure 2. A gallery of wetland images. From top to bottom left; emergent marsh in Wisconsin, black-crowned night heron
(Nycticorax nycticorax) (FWS), shrub wetland in Michigan (courtesy of St. Mary’s University), Bosque del Apache National
Wildlife Refuge, New Mexico (FWS). From top to bottom right; forested wetland (FWS), Parker River National Wildlife
Refuge, Massachusetts (FWS), freshwater wetland, northern Indiana, 2005, American toad (Bufo americanus) (Isaac
Chellman, USGS).
21
Deepwater Habitats
Wetlands and deepwater habitats are
defined separately by Cowardin et
al. (1979) because the term wetland
does not include deep, permanent
water bodies. Deepwater habitats
are permanently flooded land lying
below the deepwater boundary of
wetlands (Figure 3). Deepwater
habitats include environments where
surface water is permanent and
often deep, so that water, rather
than air, is the principal medium in
which the dominant organisms live,
whether or not they are attached to
the substrate. For the purposes of
conducting status and trends work,
all lacustrine (lake) and riverine
(river) waters were considered
deepwater habitats.
Upland Habitats
An abbreviated upland classification
system patterned after the U. S.
Geological Survey land classification
scheme described by Anderson
et al. (1976), with five generalized
categories, was used to describe
uplands in this study. These
categories are listed in Table 1.
Figure 3. Open water lakes, such as this
reservoir were classified as deepwater
habitats if they exceeded 20 acres (8 ha).
Piney Run Lake, Maryland, 2005.
22
Table 1. Wetland, deepwater, and upland categories used to conduct wetland status and trends studies.
The definitions for each category appear in Appendix A.
Category Common Description
Salt Water Habitats
Marine Subtidal* Open ocean
Marine Intertidal Near shore
Estuarine Subtidal* Open-water/bay bottoms
Estuarine Intertidal Emergents Salt marsh
Estuarine Intertidal Forested/Shrub Mangroves or other estuarine shrubs
Estuarine Unconsolidated Shore Beaches/bars
Estuarine Aquatic Bed Submerged or floating estuarine vegetation
Riverine* (may be tidal or nontidal) River systems
Freshwater Habitats
Palustrine Forested Forested swamps
Palustrine Shrub Shrub wetlands
Palustrine Emergents Inland marshes/wet meadows
Palustrine Unconsolidated Shore Shore beaches/bars
Palustrine Unconsolidated Bottom Open-water ponds
Palustrine Aquatic Bed Floating aquatic/submerged vegetations
Palustrine Farmed Farmed wetland
Lacustrine* Lakes and reservoirs
Uplands
Agriculture Cropland, pasture, managed rangeland
Urban Cities and incorporated developments
Forested Plantations Planted or intensively managed forests, silviculture
Rural Development Non-urban developed areas and infrastructure
Other Uplands (see further explanation in Appendix A) Rural uplands not in any other category; barren lands
*Deepwater habitat
23
Sampling Design
This study measured wetland extent
and change using a statistically
stratified, simple random sampling
design, the foundations of which
are well documented (Dahl 2000;
USFWS 2004b). The sampling
design used for this study was
developed by an interagency
group of spatial sampling experts
specifically to monitor wetland
change. It can be used to monitor
conversions between ecologically
different wetland types, as well as
measure wetland gains and losses.
Sample plots were examined, with
the use of remotely sensed data
in combination with field work,
to determine wetland change.
To monitor changes in wetland
area, the 48 conterminous states
were stratified or divided by state
boundaries and 35 physiographical
subdivisions described by Hammond
(1970) (Appendix B).
Monitoring Wetlands
Stratification of the nation based on
differences in wetland density makes
this study an effective measure of
wetland resources. Some natural
resource assessments stop at county
boundaries or at a point coinciding
with the census line for inhabitable
land area. Doing so may exclude
offshore wetlands, shallow water
embayments or sounds, shoals, sand
bars, tidal flats and reefs (Figure
4). These are important fish and
wildlife habitats.
The Fish and Wildlife Service
included wetlands in coastal areas
by adding a supplemental sampling
stratum along the Atlantic and
Gulf coastal fringes. This stratum
includes the near shore areas of the
coast with its barrier islands, coastal
marshes, exposed tidal flats and
other offshore features not a part of
the landward physiographic zones.
The coastal zone stratum, included
28.2 million acres (11.4 million ha).
At its widest point in southern
Louisiana, this zone extended about
92.6 miles (149 km) from Lake
24
Figure 4. Coastal wetlands offshore from the mainland, include salt marsh (estuarine emergent) (A), shoals (B), tidal flats (C)
and bars. National Aerial Photography Program, color infrared photograph,coastal Louisiana, 2004.
Pontchartrain to the furthest extent
of estuarine wetland resources.
In this area, saltwater was the
overriding influence on biological
systems. The coastal zone in this
study was not synonymous with any
state or federal jurisdictional coastal
zone definitions. The legal definition
of “coastal zone” has been developed
for use in coastal demarcations,
planning, regulatory and
management activities undertaken
by other federal or state agencies.
To permit even spatial coverage
of the sample plots and to allow
results to be computed easily by
sets of states, the 36 physiographic
regions formed by the Hammond
subdivisions and the coastal zone
stratum were intersected with state
boundaries to form 220 subdivisions
or strata. An example of this
stratification approach and the way
it relates to sampling frequency is
shown for North Carolina (Figure 5).
In the physiographic strata
described above, weighted, stratified
sample plots were randomly
allocated in proportion to the amount
of wetland acreage expected to occur
in each stratum. Each sample area
was a surface plot 2.0 miles (3.2
km) on a side or 4.0 square miles
of area equaling 2,560 acres (1,036
ha). The study included all wetlands
regardless of land ownership.
This study re-analyzed the land area
for 4,371 existing sample plots used
for past wetlands status and trends
studies. Three hundred eleven
supplemental sample plots were
added to Ohio, Indiana, Illinois,
Iowa, Missouri, North Dakota,
South Dakota, California, Oklahoma
and Texas. Augmentation was done
to provide more finite measurement
and equitable spatial coverage of
plots, since loss rates had been
declining historically. This brought
the total number of sample plots
used in this study to 4,682.
25
Figure 5. Physiographic subdivisions of North Carolina and sample plot distribution as used in this study.
Sample Plot Location
Dry
Wet
Gulf-Atlantic Rolling Plain
Appalachian
Highlands
Gulf-Atlantic Coastal Flats
Coastal
Zone
Types and Dates
of Imagery
Image analysts relied primarily
on observable physical or spectral
characteristics evident on high
altitude imagery, in conjunction with
collateral data, to make decisions
regarding wetland classification and
deepwater determinations .
3Analysis of imagery was supplemented
with substantial field work and ground
observations.
Figure 6. High resolution, infrared Ikonos satellite image of bogs (A), lakes (B) and wetlands (C) of northern Wisconsin, spring
2005. Image courtesy of Space Imaging Corp.
Remote sensing techniques to detect
and monitor wetlands in the United
States and Canada have been used
successfully by a number academic
researchers and governmental
agencies (Dechka et al. 2002;
Watmough et al. 2002; Tiner 1996;
National Research Council 1995;
Patience and Klemas 1993; Lillesand
and Kiefer 1987; Aldrich 1979). The
use of remotely sensed data, either
from aircraft or satellite, is a cost
effective way to conduct surveys
over expansive areas (Dahl 1990a).
The Fish and Wildlife Service has
used remote sensing techniques to
determine the biological extent of
wetlands for the past 30 years. To
monitor wetland change, only high
quality imagery was acquired and
used.
26
This study used multiple sources
of recent imagery and direct on-the-
ground observations to record
wetland changes. To recognize and
classify wetland vegetation, color
infrared imagery was preferred
(Figure 6). Experienced wetland
interpreters have found color
infrared to be superior to other
imagery types for recognition and
classification of wetland vegetation
types (USFWS 2004b).
Figure 7. Early spring 2005 Ikonos satellite image of Michigan. Leaf-off condition made recognition of wetland features easier.
These old oxbows or swales (indicated by red arrows) can be masked by heavy tree canopy later in the growing season. Image
courtesy of Space Imaging Corp.
Wherever possible, leaf-off (early
spring or late fall) imagery was
used. Imagery obtained when
vegetation was dormant allowed
for better identification of wetland
boundaries, areas covered by water,
drainage patterns, separation of
coniferous from deciduous forest,
and classification of some understory
vegetation (Tiner 1996). There are
distinct advantages to using leaf-off
imagery to detect the extent of
forested wetlands. Leaf off imagery
enhances the visual evidence of
hydrologic conditions such as
saturation, flooding, or ponding
(Figure 7). This imagery, combined
with collateral data including soil
surveys, topographic maps, and
wetland maps were used to identify
and delineate the areal extent of
wetlands.
27
Figure 8. Mean date of imagery used by state.
In 2004, recent aerial photographic
coverage for large portions of the
country was not available. Multiple
sources of satellite imagery in
combination with recently acquired
digital photography were used
to complete this study. Satellite
imagery made up about 45 percent
of the source material used for
this analysis. Advantages included
higher resolution digital imagery
that was acquired close to the target
reporting date. The mean dates
of the imagery used, by state, are
shown in Figure 8.
Satellite imagery was supplemented
with National Agriculture Imagery
Program (NAIP) imagery acquired
during the agricultural growing
season (Figure 9). NAIP imagery
made up about 30 percent of the
source imagery. (For technical
specifications of NAIP imagery
see www.apfo.usda.gov/NAIP/ .)
The remaining imagery needed to
complete the study was acquired
through various sources of high
resolution aerial photography.
28
2003
2004
2005
California
Oregon
Idaho
Montana
Wyoming
Nevada
Utah
Colorado
North Dakota
South Dakota
Nebraska
Kansas Missouri
Illinois
Wisconsin
Michigan
Indiana
Ohio
Kentucky
Virginia
Florida
South
Carolina
Georgia
North
Carolina
Pennsylvania
New Jersey
New Hampshire
Maryland
Delaware
Connecticut
Massachusetts
Vermont Maine
New York
Rhode Island
West
Virginia
Tennessee
Mississippi
Alabama
Arkansas
Louisiana
Texas
Iowa
Minnesota
Oklahoma
New Mexico
Arizona
Washington
Figure 9. True color NAIP photographs show
farmland (A), forest (B) and wetlands (C) above, and
newly-created ponds in a housing development (D) at
right. Indiana, 2003.
29
Figure 10. A small wetland basin estimated to have been about seven square meters. Some
wetlands this size were detectable using high resolution imagery.
Technological
Advances
Technological advances in the
quality of remotely sensed
imagery, computerized mapping
techniques, and modernization of
data management systems enhanced
the ability to capture more detailed
and timely information about the
nation’s wetlands. The use of these
technologies greatly improved the
administration, access, management
and integration of the spatial
data. Such advances required
modernization of procedural
techniques for image interpretation,
data capture and operational
management. Some of the data
modernization process involved
development of customized software
tools to execute tasks specific to
wetland attribution, provide logic
checking functions and verification
of the digital status and trends data.
These procedural updates were
incorporated into a revised technical
procedures and protocols manual
(USFWS 2004b).
Methods of Data
Collection and
Image Analysis
The delineation of wetlands through
image analysis forms the foundation
for deriving all subsequent products
and results. Consequently, a
great deal of emphasis has been
placed on the quality of the image
interpretation. The Fish and
Wildlife Service makes no attempt
to adapt or apply the products of
these techniques to regulatory or
legal authorities regarding wetland
boundary determinations or to
jurisdiction or land ownership, but
rather the information was used to
assist in making trend estimates
characterizing wetland habitats.
General information on photo
interpretation techniques is
provided by various authors (Avery
1968; Lillesand and Kiefer 1987;
Philipson 1996). Specific protocols
used for image interpretation of
wetlands are documented in the
Status and Trends technical manual
(USFWS 2004b).
Wetlands were identified based on
vegetation, visible hydrology and
geography. Delineations on the
sample plots reflected ecological
change or changes in land use that
influenced the size, distribution or
classification of wetland habitats.
The minimum targeted delineation
unit for wetland was one acre
(0.40 ha). The actual smallest size
of wetland features delineated
was about 0.005 acres (0.002 ha).
However, not all features this size,
or smaller, were detected (Figure
10).
30
Wetland Change
Detection
Remotely sensed imagery was the
primary data for wetland change
detection. It was used in conjunction
with reliable collateral data such
as topographic maps, coastal
navigation charts, soils information,
and historical imagery or studies.
Field verification also played an
important role and was used to
address questions regarding image
interpretation, land use classification
and attribution of wetland gains or
losses.
For each sample plot, the extent
of change among all wetland types
between the two dates of imagery
was used to estimate the total area
of each wetland type (Figure 11)
and the changes in wetland area and
type between the two dates. The
changes were recorded in categories
that can be considered the result
of either natural change, such as
the natural succession of emergent
wetlands to shrub wetlands, or
human induced change. Areas of
sample plots that were identified
in the initial era as wetland but are
no longer wetland were placed into
five land use categories (agriculture,
upland forested plantations,
upland areas of rural development,
upland urban landscapes and other
miscellaneous lands) based upon
the land use evident on the most
recent imagery. The outputs from
this analysis were change matrices
that provided estimates of wetland
area by type and observed changes
Figure 11. Change detection involved a comparison of plots at two different times (T1 and T2).
over time. Rigorous quality control
inspections were built into the
interpretation, data collection and
analysis processes.
Difficulties in determining wetland
change can be related to timing
or quality of the imagery (Dahl
2004). Imagery acquired at the
time of abnormal hydrologic
conditions, such as flooding or
drought, can make determination
of wetland change challenging.
In these instances field work was
required to assist image analysts
in making appropriate wetlands
determinations.
Misinterpretation of wetland loss or
gain could result from factors such
as farming of wetlands during dry
cycles, drought conditions, excess
T1 T2
6 years
31
surface water or flooding. False
changes were avoided by observing
visual evidence of a change in
land management practices. This
included the presence of new
drainage ditches (Figure 12),
canals or other man-made water
courses, evidence of dredging, spoil
deposition or fills, impoundments or
excavations, structures, pavement or
hardened surfaces, in addition to the
lack of any hydrology, vegetation or
soil indicators indicative of wetland.
Some land use practices can also
affect wetland change detection.
Disturbed sites often had ambiguous
remotes sensing indicators.
Disturbed areas were indicative
of lands in transition from one
Figure 13. Lands in transition from
one land use category to another pose
unique challenges for image analysts.
Field inspection of this site indicated
the area was under construction as part
of a highway project.
land use to another (Figure 13).
Upon field inspection, these areas
often had altered hydrology,
soils or vegetation making
wetland classification and change
determination more difficult. In
these instances, field inspection of
the wetland site and surrounding
area provided additional
information.
Figure 12. A true color aerial
photograph shows a new drainage
network (indicated by red arrow)
and provides visual evidence of
wetland loss. Lack of wetland
vegetation, surface water or soil
saturation further indicates that
this wetland had been effectively
drained.
32
Field
Verification
Field verification was completed
for 1,504 (32 percent) of the sample
plots distributed in 35 States
(Figure 14). This constituted
the largest field verification
effort undertaken for a status
and trends report. Field work
was done primarily as a quality
control measure to verify that
plot delineations were correct.
Verification involved field visits to a
cross section of wetland types and
geographic settings, and to plots
with different image types, scales
and dates. Field work was not done
in some western states because of
the remote location (limited access)
of sample plots. Of the 1,504 sample
plots reviewed in the field, 720 used
satellite imagery and 784 used high
altitude aerial photography. All
field verification work took place
between March and September,
2005 . Representatives from four
states and seven federal agencies
participated in field reconnaissance
trips. In rare instances, field work
was used to update sample plots
based on observations of on-the-ground
conditions.
4 Results of field verification work indicated
no discernable differences in the size or
classification of wetlands delineated using
either satellite imagery or the high altitude
photography. Errors of wetland omission
were two percent based on occurrence
but less than one percent based on area
(omitted wetlands were generally small <
1.0 acre or 2.47 ha). Errors of inclusion of
upland were less than one percent in both
occurrence and area. There was no difference
regionally, between states or data analysts
in the number of errors found based on
field inspections, although not all plots were
included in the field analysis.
Figure 14. Field verification was completed at sites in 35 states shown on the map.
33
States not field verified
States field verified
California
Oregon
Idaho
Montana
Wyoming
Nevada
Utah
Colorado
North Dakota
South Dakota
Nebraska
Kansas Missouri
Illinois
Wisconsin
Michigan
Indiana
Ohio
Kentucky
Virginia
Florida
South
Carolina
Georgia
North
Carolina
Pennsylvania
New Jersey
New Hampshire
Maryland
Delaware
Connecticut
Massachusetts
Vermont Maine
New York
Rhode Island
West
Virginia
Tennessee
Mississippi
Alabama
Arkansas
Louisiana
Texas
Iowa
Minnesota
Oklahoma
New Mexico
Arizona
Washington
Quality Control
To ensure the reliability of wetland
status and trends data, the Fish
and Wildlife Service adhered to
established quality assurance and
quality control measures for data
collection, analysis, verification and
reporting. Some of the major quality
control steps included:
Plot Location and Positional
Accuracy
Status and trends sample plots were
permanently fixed georeferenced
areas used to monitor land use and
cover type changes. The same plot
population has been re-analyzed
for each status and trends report
cycle. The plot coordinates were
positioned precisely using a system
of redundant backup locators on
prints produced from a geographic
information system, topographic
maps (Figure 15), other maps
used for collateral information and
the aerial imagery. Plot outlines
were computer generated for the
correct spatial coordinates, size and
projection (Figure 16).
Quality Control of Interpreted Images
This study used well established,
time-tested, fully documented data
collection conventions (USFWS
1994a; 1994b; 2004b). It employed
a small cadre of highly skilled and
experienced personnel for image
interpretation and processing.
All interpreted imagery was
reviewed by a technical expert in
ecological change detection. The
reviewing analyst adhered to all
standards, quality requirements and
technical specifications and reviewed
100 percent of the work.
Data Verification
All digital data files were subjected
to rigorous quality control
inspections. Digital data verification
included quality control checks
that addressed the geospatial
correctness, digital integrity and
some cartographic aspects of
the data. These steps took place
following the review and qualitative
acceptance of the ecological data.
Implementation of quality checks
ensured that the data conformed to
the specified criteria, thus achieving
the project objectives.
Quality Assurance of Digital Data
Files
There were tremendous advantages
in using newer technologies to store
and analyze the geographic data.
The geospatial analysis capability
built into this study provided a
complete digital database to better
assist analysis of wetland change
information.
All digital data files were subjected
to rigorous quality control
inspections. Automated checking
modules incorporated in the
geographic information system
(Arc/GIS) were used to correct
digital artifacts including polygon
topology. Additional customized
data inspections were made to
ensure that the changes indicated
at the image interpretation stage
were properly executed. Digital file
quality control reviews also provided
confirmation of plot location,
stratum assignment, and total land
or water area sampled.
A customized digital data
verification software package
designed specifically for status
and trends work was used. It
checked for improbable changes
that may represent errors in the
image interpretation. The software
considered the length of time
between update cycles, identified
certain unrealistic cover-type
changes such open water ponds
changing to forested wetland, and
other types of potential errors in the
digital data.
34
Figure 15. Topographic maps in digital
raster graphics format were used as
auxilliary information and for quality
control.
Figure 16. Digital wetlands status and trends data were viewed combined with contemporary georeferenced color infrared
imagery of the study areas.
35
Statistical
Analysis
The wetland status and trends
study was based on a scientific
probability sample of the surface
area of the 48 conterminous States.
The area sampled was about 1.93
billion acres (0.8 billion ha), and
the sampling did not discriminate
based on land ownership. The study
used a stratified, simple random
sampling design. About 754,000
possible sample plots comprised
the total population. Given this
population, the sampling design was
stratified by use of the 36 physical
subdivisions described in the “Study
Design” section. This stratification
scheme had ecological, statistical,
and practical advantages. The
study design was well suited for
determining wetland acreage trends
because the 36 divisions of the
United States coincide with factors
that effect wetland distribution
and abundance. Once stratified,
the land subdivisions represented
large areas where the samples were
distributed to obtain an even spatial
representation of plots. The final
stratification, based on intersecting
physiographic land types with state
boundaries, guaranteed an improved
spatial random sample of plots.
Geographic information system
software organized the information
about the 4,682 random sample
plots. An important design feature
crucial to understanding the
technical aspects of this study is
that a grid of full-sized square plots
can be overlaid on any stratum to
define the population of sampling
units for that stratum. However, at
the stratum boundaries some plots
were “split” across the boundary
and thus, were not a full 2,560 acres
(1,036 ha). In sampling theory, plot
size is an auxiliary variable that is
known for all sampled plots and
whose total is known over every
stratum. All sampling units (plots) in
a stratum were given equal selection
probabilities regardless of their
size. In the data analysis phase, the
adjustments were made for varying
plot sizes by use of ratio estimation
theory. For any wetland type, the
proportion of its area in the sample
of plots in a stratum was an unbiased
estimator of the unknown proportion
of that type in that stratum.
Inference about total wetland
acreage by wetland type or for all
wetlands in any stratum began with
the ratio (r) of the relevant total
acreage observed in the sample (Ty),
for that stratum divided by the total
area of the sample (Tx). Thus, y
was measured in each sample plot;
r = Ty/Tx, and the estimated total
acreage of the relevant wetland type
in the stratum was A x r. The sum
of these estimated totals over all
strata provided the national estimate
for the wetland type in question.
Uncertainty, which was measured
as sampling variance of an estimate,
was estimated based on the variation
among the sample proportions in a
stratum (the estimation of sample
variation is highly technical and
not presented here). The sampling
variation of the national total was
the sum of the sampling variance
over all strata. These methods are
standard for ratio estimation in
association with a stratified random
sampling design (Sarndal et al. 1992;
Thompson 1992).
By use of this statistical procedure,
the sample plot data were expanded
to specific physiographic regions,
by wetland type, and statistical
estimates were generated for the 48
conterminous States. The reliability
of each estimate generated is
expressed as the percent coefficient
of variation (% C.V.) associated with
that estimate. Percent coefficient of
variation was expressed as (standard
deviation/mean) x (100). The percent
coefficient of variation indicates that
there was a 95 percent probability
that an estimate was within the
indicated percentage range of the
true value.
Procedural Error
Procedural or measurement errors
occur in the data collection phase of
any study and must be considered.
Procedural error is related to the
ability to accurately recognize
and classify wetlands both from
multiple sources of imagery and
on-the-ground evaluations. Types of
procedural errors may have included
missed wetlands, inclusion of
upland as wetland, misclassification
of wetlands or misinterpretation
of data collection protocols. The
amount of introduced procedural
error is usually a function of the
quality of the data collection
conventions; the number, variability,
training and experience of data
collection personnel; and the rigor
of any quality control or quality
assurance measures.
Rigorous quality control reviews
and redundant inspections were
incorporated into the data collection
and data entry processes to help
reduce the level of procedural error.
Estimated procedural error ranged
from 3 to 5 percent of the true values
when all quality assurance measures
had been completed.
36
Limitations
The identification of wetland
habitats through image analysis
forms the basis for wetland status
and trends data results. Because of
the limitations of aerial imagery as
the primary data source to detect
some wetlands, the Fish and Wildlife
Service excludes certain wetland
types from its monitoring efforts.
These limitations included the
inability to detect small areas;
inability to accurately map or
monitor certain types of wetlands
such as sea grasses (Orth et
al. 1990), submerged aquatic
vegetation, or submerged reefs
(Dahl 2005); and inability to
consistently identify certain forested
wetlands (Tiner 1990).
Other habitats intentionally
excluded from this study include:
Estuarine wetlands of the Pacific
coast—Unlike the broad expanses
of emergent wetlands along the
Gulf and Atlantic coasts, the
estuarine wetlands of California,
Oregon and Washington occur in
discontinuous patches (Figure
17). Their patchy distribution
precludes establishment of a coastal
stratum similar to that of the Gulf
and Atlantic coast wetlands and
no statistically valid data could be
obtained through establishment of a
Pacific coastal stratum. Therefore,
consistent with past studies, this
study did not sample Pacific coast
estuarine wetlands such as those
in San Francisco Bay, California;
Coos Bay, Oregon; or Puget Sound,
Washington.
Figure 17. The Pacific coastline, Three Arch Rocks National Wildlife Refuge, Oregon. Photo courtesy of FWS.
37
Figures 18A and B. Commercial rice
fields where water was pumped to flood
the rice crop. These fields were drained
when they were in upland crop rotation.
Central Arkansas, 2005.
Commercial Rice—Throughout
the southeastern United States and
in California, rice (Oryza sativa)
is planted on drained hydric soils
and on upland soils. When rice was
being grown, the land was flooded
and the area functioned as wetland
(Figures 18A and B). In years when
rice was not grown, the same fields
were used to grow other crops (e.g.,
corn, soybeans, cotton). Commercial
rice lands were identified primarily
in California, Arkansas, Louisiana,
Mississippi and Texas. These
cultivated rice fields were not able
to support hydrophytic vegetation.
Consequently, the Fish and Wildlife
Service did not include these lands in
the base wetland acreage estimates.
38
A
B
Agricultural activity was shown by
distinctive geometric field and road
patterns on the landscape and/or
by tracks produced by livestock or
mechanized equipment. Agricultural
land uses included horticultural
crops, row and close grown crops,
hayland, pastureland, native
pastures and range land and farm
infrastructures (Figure 19A and B).
Examples of agricultural activities in
each land use include:
Horticultural crops consisted of
orchard fruits (limes, grapefruit,
oranges, other citrus, apples,
peaches and like species). Also
included were nuts such as almonds,
pecans and walnuts; vineyards
including grapes and hops; bush-fruit
such as blueberries; berries such
as strawberries or raspberries; and
commercial flower and fern growing
operations.
Attribution of
Wetland Losses
The process of identifying or
attributing cause for wetland losses
or gains has been investigated by
both the Fish and Wildlife Service
and Natural Resources Conservation
Service. In 1998 and 1999, the
Natural Resources Conservation
Service and the Fish and Wildlife
Service made a concerted effort
to develop a uniform approach to
attribute wetland losses and gains
to their causes. The categories used
to determine the causes of wetland
losses and gains are described below.
Agriculture
The definition of agriculture
followed Anderson et al. (1976)
and included land used primarily
for production of food and fiber.
Row and Close Grown Crops
included field corn, sugar cane,
sweet corn, sorghum, soybeans,
cotton, peanuts, tobacco, sugar
beets, potatoes, and truck crops
such as melons, beets, cauliflower,
pumpkins, tomatoes, sunflower and
watermelon. Close grown crops also
included wheat, oats, barley, sod,
ryegrass, and similar graminoids.
Hayland and pastureland included
grass, legumes, summer fallow and
grazed native grassland.
Other farmland included
farmsteads and ranch headquarters,
commercial feedlots, greenhouses,
hog facilities, nurseries and poultry
facilities.
Figure 19A and B. Examples of agricultural land use include both
this rangeland in western Nebraska, 2005 (A), and row crops such
as this cornfield in the midwest, 2004 (B).
39
A
B
Forested Plantations
Forested plantations consisted
of planted and managed forest
stands and included planted pines,
Christmas tree farms, clear cuts and
other managed forest stands. These
were identified by the following
remote sensing indicators: 1) trees
planted in rows or blocks; 2) forested
blocks growing with uniform crown
heights; or 3) logging activity and
use patterns (Figure 20).
Figure 20. Trees planted in rows with uniform crown height (A) and block clear cuts [blue-green feature in center (B) were
indicators of managed forest plantations. Color infrared Ikonos satellite image, Virginia 2004. Courtesy of Space Imaging Corp.
Rural Development
Rural developments occurred in
rural and suburban settings outside
distinct cities and towns. They were
characterized by non intensive land
use and sparse building density.
Typically, a rural development was
a crossroads community that had a
corner gas station and a convenience
store and was surrounded by
sparse residential housing.
Scattered suburban communities
located outside of a major urban
centers were also included in this
category as were some industrial
and commercial complexes;
isolated transportation, power,
and communication facilities; strip
mines; quarries; and recreational
areas such as golf courses.
Major highways through rural
development areas were included in
the rural development category.
40
Urban Development
Urban land consisted of areas of
intensive use in which much of the
land was covered by structures
(high building density as shown in
Figure 21). Urbanized areas were
cities and towns that provided
goods and services through a
central business district. Services
such as banking, medical and legal
office buildings, supermarkets and
department stores made up the
business center of a city. Commercial
strip developments along main
transportation routes, shopping
centers, contiguous dense residential
areas, industrial and commercial
complexes, transportation, power
and communication facilities, city
parks, ball fields and golf courses
were included in the urban category.
Other Land Uses
Other Land Use was composed
of uplands not characterized by
the previous categories. Typically
these lands included native prairie,
unmanaged or non patterned upland
forests, conservation lands, scrub
lands, and barren land. Lands in
transition between different uses
were also in this category.
Transitional lands were lands in
transition from one land use to
another. They generally occurred
in large acreage blocks of 40
acres (16 ha) or more. They were
characterized by the lack of any
remote sensor information that
would enable the interpreter to
reliably predict future use. The
transitional phase occurred when
wetlands were drained, ditched,
filled or when the vegetation had
been removed and the area was
temporarily bare.
Interagency field evaluations were
conducted to test these definitions
on the wetland status and trends
plots to attribute wetland losses or
gains. Field evaluation of these plots
resulted in no disagreement among
agency representatives with how the
Fish and Wildlife Service attributed
wetland losses or gains as to cause.
Figure 21. Urban wetlands (shown as dark blue-black) outside of a shopping mall are surrounded by high density urban
development. New Jersey, 2003, color infrared photograph.
41
A freshwater wetland, Reelfoot Lake, Tennessee, 2005.
42
Results and Discussion
Status of the Nation’s Wetlands
There were an estimated 107.7
million acres (43.6 million ha) of
wetlands in the conterminous
United States in 2004 . (The
coefficient of variation of the
national estimate was 2.7
percent. ) Wetlands composed
5.5 percent of the surface area
of the conterminous United
States (Figure 22). An estimated
95 percent of all wetlands were
freshwater and five percent were
in estuarine or marine systems.
This overall distribution of
wetlands by area and type had not
changed from the previous era.
5 This estimate reflects a 2.0 percent
adjustment to the national wetland acreage
base. This adjustment is within the 3
percent coefficient of variation associated
with this estimation.
6 95 percent confidence interval
Figure 22. Wetland area compared to the total land area of the
conterminous United States, 2004.
Data for the 1998 to 2004 study
period are presented in a change
matrix and shown in Appendix C.
For ease of use, those data have
been summarized and presented in
Table 2.
Within the estuarine system,
estuarine emergent (salt marsh—
Figure 23) dominated, making up
an estimated 73 percent (almost 3.9
million acres or 1.6 million ha) of
all estuarine and marine wetlands.
Estuarine shrub wetlands made
up 13 percent of the area and non-vegetated
saltwater wetlands 14
percent (Figure 24).
Among freshwater wetlands (Figure
25), freshwater forested wetlands
made up the single largest category
(51 percent). Freshwater emergent
wetland made up an estimated 25.5
percent of the total area, shrub
wetlands 17 percent and freshwater
ponds 6.5 percent.
43
Upland
93.5%
Total Land Area
Deepwater*
1%
Wetland
5.5%
*Excludes area of the
Great Lakes
Table 2. Change in wetland area for selected wetland and deepwater categories, 1998 to 2004. The coefficient of
variation (CV) for each entry (expressed as a percentage) is given in parentheses.
Area, In Thousands of Acres
Wetland/Deepwater Category Estimated Area,
1998
Estimated Area,
2004
Change,
1998–2004
Change
(In Percent)
Marine 130.4
(20.2)
128.6
(20.5)
–-1/9
(68.7) –1.4
Estuarine Intertidal Non-Vegetated1 594.1
(10.7)
600.0
(10.3)
5.9
* 1.0
Estuarine Intertidal Vegetated2 4,604.2
(4.0)
4,571.7
(4.0)
–32.4
(32.7) –0.7
All Intertidal Wetlands 5,328.7
(3.8)
5,300.3
(3.8)
–28.4
(48.6) –0.5
Freshwater Non-Vegetated3 5,918.7
(3.7)
6,633.9
(3.5)
715.3
(12.8) 12.1
Freshwater Ponds4 5,534,3
(3.7)
6,229.6
(3.5)
695.4
(13.1) 12.6
Freshwater Vegetated5 96,414.9
(3.0)
95,819.8
(3.0)
–495.1
(35.0) –0.5
Freshwater Emergent 26,289.6
(8.0)
26,147.0
(8.0)
–142.6
* –0.5
Freshwater Forested 51,483.1
(2.8)
52,031.4
(2.8)
548.2
(56.1) 1.1
Freshwater Shrub 18,542.2
(4.1)
17,641.4
(4.3)
–900.8
(34.2) –4.9
All Freshwater Wetlands 102,233.6
(2.9)
102,453.8
(2.8)
220.2
(77.3) 0.2
All Wetlands 107,562.3
(2.7)
107,754.0
(2.7)
191.8
(89.1) 0.2
Deepwater Habitats
Lacustrine5 16,610.5
(10.4)
16,773.4
(10.2)
162.9
(76.2) 1.0
Riverine 6,765.5
(9.1)
6,813.3
(9.1)
47.7
(68.8) 0.7
Estuarine Subtitdal 17.680.5
(2.2)
17.717.8
(2.2)
37.3
(40.8) 0.2
All Deepwater Habitats 41,046.6
(4.6)
41,304.5
(4.5)
247.9
(51.7) 0.6
All Wetlands and Deepwater Habitats1,2 148,618.8
(2.4)
149,058.5
(2.4)
439.7
(31.3) 0.3
*Statistically unreliable.
1 Includes the categories: Estuarine Intertidal Aquatic Bed and Estuarine Intertidal Unconsolidated Shore.
2 Includes the categories: Estuarine Intertidal Emergent and Estuarine Intertidal Shrub.
3 Includes the categories: Palustrine Aquatic Bed, Palustrine Unconsolidated Bottom and Palustrine Unconsolidated Shore.
4 Includes the categories: Palustrine Aquatic Bed, Palustrine Unconsolidated Bottom.
5 Includes the categories: Palustrine Emergent, Palustrine Forested and Palustrine Shrub.
6 Does non include the open-water area of the Great Lakes.
Percent coefficient of variation was expressed as (standard deviation/mean) x 100.
44
Figure 24. Percentage of
estimated estuarine and
freshwater wetland area and
covertypes, 2004.
Figure 23. Salt marsh along the Ecofina
River, Florida.
Figure 25. A freshwater wetland in the
southeastern United States, 2005.
Estuarine Wetlands
Total Wetlands
Freshwater
95%
Estuarine
5%
Emergents
73%*
Flats/Beaches
14%
Shrubs
13%
Freshwater Wetlands
Forested
51%
Emergents
25.5%*
Shrubs
17%
Ponds
6.5%
*Denotes change from
previous era
45
National Trends, 1998 to 2004
Between 1998 and 2004 there was
an estimated net gain (Table 3) in
wetlands of 191,750 acres (77,630
ha). This equated to an average
annual net gain of about 32,000
acres (12,900 ha) as seen in Figure
26. These estimates have led to the
conclusion that wetland area gains
achieved through restoration and
creation have outdistanced losses.
These data indicate a net gain in
acreage but this report does not
draw conclusions regarding trends
in quality of the nation’s wetlands
7 There are statistical uncertainties associated
with this estimate. The coefficient of variation
expressed as a percentage is 89.1 percent for
the net gain estimate.
Intertidal wetlands declined by
an estimated 28,416 ac (11,500 ha)
from 1998 to 2004. This was an
average annual loss of about 4,740
acres (1,920 ha). The majority of
these losses (94 percent) were to
deepwater bay bottoms or open
ocean.
Almost all net gains of wetland
observed between 1998 and 2004
were in freshwater wetland types.
The estimated net gain in freshwater
wetland area between 1998 and 2004
was 220,200 acres (89,140 ha) as
Figure 26. Average annual net loss and gain estimates for the conterminous United States, 1954 to 2004. Sources: Frayer et al.
1983; Dahl and Johnson 1991; Dahl 2000; and this study.
seen in Table 2. Forested wetlands
experienced a net gain. This can
be explained by the maturation of
wetland shrubs to forested wetlands.
There was also a substantial increase
in the number of open water ponds.
Pond area increased by an estimated
12.6 percent over this study period.
46
100,000
0
-100,000
-200,000
-300,000
-400,000
-500,000
Gains
+32,000
Losses
-58,550
-290,000
-458,000
1950s–1970s 1970s–1980s 1980s–1990s
Acres
1998–2004
Attribution of
Wetland Gain
and Loss
Figure 27 depicts the categories
that contributed wetland gains and
those responsible for wetland losses
over the course of this study. A net
gain in wetland area was attributed
to conversion of agricultural lands
or former agricultural lands that
had been idled in combination
with wetland restorations from
conservation lands in the “other”
land use category.
Some freshwater wetland
losses attributed to urban, rural
development and silviculture offset
some of the gains. An estimated
88,960 acres (36,000 ha) or 39
percent of the wetland losses, were
lost to urban developments, 51,440
acres (20,800 ha), 22 percent were
lost to rural development and
18,000 acres (7,300 ha), 8 percent
of wetlands were lost through
drainage or filling for silviculture.
These losses were all the result of
actions that destroyed the wetland
hydrology. An additional 70,100
acres (28,400 ha), or 31 percent
of the wetland area lost between
1998 and 2004 became deepwater
habitats.
There were net gains from the
“other” lands category and from
Agriculture as a result of wetland
restoration and conservation
programs. An estimated 70,700
wetland acres (28,600 ha) came from
agricultural lands and 349,600 acres
(141,500 ha) from “other” uplands.
These gains represented 17 percent
of the net wetland gains from
Agriculture and 83 percent from
“other” uplands. Since the “other”
uplands category includes lands in
transition some of these wetlands
may be subject to loss over time.
Representative wetland restoration
programs are listed in Appendix D.
Using the study definitions for
the causes of wetland losses and
gains, it was determined that urban
development and rural development
accounted for an estimated 140,400
acres (56,840 ha) or 61 percent of
wetland loss over the course of this
study.
Figure 27. Wetlands gained or lost from upland categories and deepwater, 1998 to 2004.
47
Deepwater
-70,100
Urban
-88,960
Rural
Development
-51,440
Land Use Category
Silviculture
-18,000
Agriculture
+70,770
Other
+349,600
0
20
-20
-40
-60
-80
-90
40
60
80
400,000
Acres (in Thousands)
Gains
Losses
Intertidal
Estuarine and
Marine Wetland
Resources
Three major categories of estuarine
and marine wetlands were included
in this study: estuarine intertidal
emergents (salt and brackish water
marshes), estuarine shrub wetlands
(mangrove swamps or mangles and
other salt tolerant woody species)
and estuarine and marine intertidal
non-vegetated wetlands. This latter
category included exposed coastal
beaches subject to tidal flooding,
shallow water sand bars, tidal flats,
tidally exposed shoals and sand
spits.
The vegetated components of the
estuarine and marine systems
are among the most biologically
productive aquatic ecosystems in
the world (Kennish 2004). Wetlands
along the nation’s coastline have
provided valuable resources and
supported large sections of the
nation’s economy (USEPA 2004).
Wetlands have also provided
opportunities for recreation and
supported commercially valuable
fish and crustacean populations.
Estuarine and wetland dependent
Figure 28. Composition of marine and estuarine intertidal wetlands, 2004.
fish and shellfish species accounted
for about 75 percent of the total
annual seafood harvest in the United
States (Weber 1995). In the Gulf of
Mexico, coastal waters attracted
millions of sport fishermen and
beach users as tourism in the Gulf
coast states contributed over $20
billion to the nation’s economy
(USEPA 1999). The importance
of both estuarine and freshwater
wetlands to fish populations, and
sport and commercial fishing
cannot be overemphasized. This
link between wetlands and aquatic
species includes ecological processes
that are important for maintaining
food webs, land and water
interactions, and environmental
quality. Wetland loss and its effect
on fish populations are among the
many issues forcing a re-evaluation
of activities on the landscape (NOAA
2001).
Estuarine and marine wetlands
have been particularly susceptible
to the various stressors resulting
from rapid population growth and
development within the coastal
watersheds nationwide (Kennish
8 The importance of wetlands to fish
populations is discussed in the insert section
“Wetlands and Fish.”
2004). From the 1950s to 1970s,
estuarine wetlands were dredged
and filled extensively for residential
and commercial development and
for navigation (Hefner 1986). To
help conserve the nation’s valuable
coastal resources, numerous
measures have been taken to protect
estuarine and marine resources.
Since the mid 1970s, many of the
nation’s shoreline habitats have
been protected either by regulation
or public ownership. These
mechanisms, in combination with
outreach and educational efforts,
have been responsible for reducing
intertidal wetlands losses in Florida
(Dahl 2005).
This study estimated that in 2004
there were slightly more than 5.3
million acres (2.1 million ha) of
marine and estuarine wetlands in
the conterminous United States.
Eighty six percent of that total area
was vegetated wetland (Figure 28).
Collectively, intertidal wetlands
declined by an estimated 28,416
ac (11,580 ha) between 1998 and
2004. Estuarine vegetated wetlands
declined by an estimated 32,400
acres (13,120 ha) between 1998
and 2004. Estuarine non-vegetated
wetlands experienced a net gain of
an estimated 4,000 ac (1,620 ha);
marine intertidal shorelines declined
by 1,900 ac (770 ha).
48
All Intertidal Wetlands
Estuarine Vegetated Wetlands
Vegetated
86%
Non-vegetated
14%
Emergents
85%
Shrubs
15%
Table 3. Changes to estuarine and marine wetlands, 1998 to 2004. The coefficient of variation (CV) for each entry
(expressed as a percentage) is given in parentheses.
Area, In Thousands of Acres
Wetland Category Estimated Area,
1998
Estimated Area,
2004
Gain or Loss,
1998–2004
Change
(In Percent)
Area (as Percent)
of All Intertidal
Wetland, 2004
Marine Intertidal 130.4
(20.2)
128.6
(20.5)
–1.9
(68.7) –1.4 2.4
Estuarine Unconsolidated Shore 563.2
(10.8)
567.5
(10.4)
4.3
* 10.7
Estuarine Aquatic Bed 30.8
(27.1)
32.4
(26.0)
1.6
(63.6) 0.6
Marine and Estuarine Intertidal
Non-Vegetated
724.5
(9.8)
728.5
(9.5)
4.0
* 0.5 13.7
Estuarine Emergent 3,922.8
(4.2)
3,889.5
(4.2)
–33.2
(31.8) 73.4
Estuarine Shrub 681.4
(12.5)
682.2
(12.5)
0.8
* 12.9
Estuarine Intertidal Vegetated1 4,604.2
(4.0)
4,571.7
(4.0)
–32.4
(32.6) –0.7 86.3
Changes in Coastal Deepwater area, 1998–2004
Estuarine Subtitdal 17,680.5
(2.2)
17,717.8
(2.2)
37.3
(40.8) — —
*Statistically unreliable.
1 Includes the categories: Estuarine Emergent and Estuarine Shrub.
Excludes marine and estuarine wetlands of California, Oregon and Washington.
Percent coefficient of variation was expressed as (standard deviation/mean) x (100).
open saltwater systems (Figure 29).
This was due to natural and man-induced
activities such as dredging,
water control, and commercial and
recreational boat traffic . The losses
of estuarine emergents exceeded the
total net loss of all other intertidal
estuarine and marine wetlands
combined.
9 Losses reported here were prior to the
hurricanes of 2005. The Fish and Wildlife
Service is preparing to conduct follow-up
studies to reassess wetland changes along the
Gulf Coast.
The changes that occurred between
1998 and 2004 in estuarine and
marine wetlands are shown in Table
3. The largest acreage change was
an estimated net loss of 33,230 acres
(13,450 ha) of estuarine emergent
wetland. The greatest percent
change was a decline of 1.4 percent
of marine intertidal wetland.
The overriding factor in the decline
of estuarine and marine wetlands
was loss of emergent salt marsh to
Figure 29. Estimated percent
loss of intertidal estuarine and
marine wetlands to deepwater and
development, 1998 to 2004.
49
Deepwater
93%
Development
7%
Marine and
Estuarine
Beaches, Tidal
Bars, Flats and
Shoals
Sand, mud or rock beaches, bars
and shoals along the interface
with tidal saltwater composed the
non-vegetated intertidal wetlands
(Figure 30). These areas were
subject to dramatic changes
resulting from coastal storms,
hurricanes, tidal surge, sea level
rise, sediment deposition or various
forms of artificial manipulation
during this study period.
Ecologically, these wetlands are
important to a variety of fish and
wildlife species. Open sandy beach
Figure 30 . Non-vegetated tidal flats grade into sparsely vegetated beach ridges. These areas are important
for a variety of birds, sea turtles and other marine life. Florida, 2000.
habitats are particularly important
to nesting, foraging and loafing
waterbirds (Kushlan et al. 2002)
(Figure 31 and 32). The green sea
turtle (Chelonia mydas) and the
loggerhead sea turtle (Caretta
caretta) also use sandy beaches
for nesting sites. Shallow water
coastal flats are important for
sport fish such as the sand sea
trout (Cynoscion arenarius),
bonefish (Albuta vulpes), and snook
(Centropomus undecimalis).
There were an estimated 728,540
acres (294,960 ha) of intertidal non-vegetated
wetlands in 2004. This
study found that from 1998 to 2004
(Table 4) marine intertidal beaches
declined by 1,900 acres (770 ha),
a 1.4 percent decline. This was
very similar to the rate of decline
observed from 1986 to 1997, when
marine beaches declined 1.7 percent.
Estuarine bars, flats and shoals
(Figure 33) increased in area over
the same timeframe. There was an
estimated increase of 4,300 acres
(1,740 ha). This increase was largely
at the expense of estuarine emergent
salt marsh which was sloughed into
deeper water bays and sounds. Land
subsidence, saltwater intrusion and
coastal erosion processes may have
contributed to these changes.
Intertidal non-vegetated wetland
changes to urban and other forms
of upland development were not
statistically significant.
50
Figure 31. Intertidal marine beaches provide important
habitat for shorebirds. These types of wetlands declined by
1.4 percent between 1998 and 2004. Coastal Louisiana, 2005.
Photo by J. Harner, USGS. Figure 32. The black-necked stilt
(Himantopus mexicanus) inhabits mud
flats, pools, back water beaches, brackish
ponds of saltwater marshes and other
wetland habitats. Photo courtesy of FWS.
Figure 33. New shoals and sand bars are continually forming in shallow water areas. This image shows a new feature
(brightest white areas) off from the coast of Virginia, 2004.
51
Estuarine
Emergent
Wetlands
Estuarine emergent wetlands
(synonymous with the term “salt
marsh”) were found close to the
shoreline and were associated with
estuaries, lagoons, embayments,
sounds and coastal barriers
(Figure 34). Salinities ranged from
hypersaline to oligohaline (Cowardin
et al. 1979). The coastal plain of
the southeastern Atlantic and Gulf
States supported expansive areas
of intertidal estuarine wetlands,
particularly emergent salt marsh.
These marshes support diverse
animal life and are extremely
productive and ecologically
important features on the coastal
landscape. The abundance and
distribution of individual species
of both animals and plants are
influenced by physical conditions
including salinity, water depth,
tidal fluctuation and temperature
variations (Chabreck 1988).
There were an estimated 3,889,500
acres (1,574,700 ha) of estuarine
emergent salt marsh wetland in
2004.
Estuarine emergent wetland
declined by 33,230 acres (13,450
ha) between 1998 and 2004. This
represented a loss of 0.9 percent
of this wetland type. The average
annual rate of estuarine emergent
loss was 5,540 acres (2,240 ha). This
rate of loss was consistent with the
rate of salt marsh loss recorded from
1986 to 1997 (Dahl 2000). Urban and
rural development activities, and
the conversion of wetlands to other
upland land uses, accounted for an
estimated loss of 1,732 acres (700 ha)
or about 3.0 percent of all losses of
estuarine emergent wetland. Most
of the losses of estuarine emergent
wetland were due to loss to deep
salt water and occurred in coastal
Louisiana (Figure 35).
Numerous restoration and
rehabilitation projects have been
undertaken in Louisiana as part
of the Coastal Wetlands Planning,
Protection and Restoration Act of
1990, to begin the process of slowing
the rate of wetland loss in that
region (Zinn and Copeland 2002).
Despite these efforts, the rate of
estuarine wetland loss has remained
constant since the mid 1980s.
Projects undertaken in Louisiana
may have restored functional value
of some wetlands. Other restoration
efforts might have been directed
toward freshwater wetlands
elsewhere within “coastal” proximity
but outside of the estuarine and
marine systems.
Figure 34. High altitude infrared photograph of salt marsh (darker mottles) offshore from coastal Georgia, 2004.
52
Estuarine Emergent Wetland Loss
0–25 Acres
26–75 Acres
76–150 Acres
151–300 Acres
Texas
Texas
Louisiana
Louisiana
Mississippi
Mississippi
Alabama
Florida
Georgia
South Carolina
North Carolina
Virginia
Maryland
Delaware
New Jersey
Connecticut
Massachusetts
Vermont
New Hampshire Maine
Rhode
Island
Pennsylvania
New York
Figure 35. Estuarine emergent losses as observed in this study
along the Atlantic and Gulf of Mexico. Inset shows close up of
Louisiana where most losses occurred between 1998 and 2004.
53
Estimates of wetland loss from
this study were contrasted with
other estimates of wetland loss
in Louisiana as seen in Table 4.
Geographic dissimilarities and
terminology differences including
“coastal” versus “estuarine,”
“wetland” versus “land loss,” and
temporal differences accounted for
some of the discrepancies. It is clear
that there has been confusion over
the region included (where), types
of wetland and/or upland included
in the estimates (what) and the
timeframe of when losses occurred
(when). This study measured
changes in marine and estuarine
wetlands from 1998 to 2004 as
described earlier.
One or more of several interrelated
factors may have contributed to
the loss of estuarine emergent
wetland, including: deficiencies in
sediment deposition, canals and
artificially created waterways,
wave erosion, land subsidence, and
salt water intrusion causing marsh
disintegration. In recognizing that
human activities have affected
wetlands in Louisiana, Williams et
al. (1995) cited an extensive system
of dredged canals and flood-control
structures constructed to facilitate
hydrocarbon exploration and
production as well as commercial
and recreational boat traffic that had
enabled salt water to intrude from
the Gulf of Mexico as major factors
in wetland loss.
Coastal storms often have had a
role in destabilizing salt marsh
substrates by washing away
sediment with wind driven
floodwaters (Chabreck 1988).
Estimates of estuarine emergent
area reported here, were made
prior to Hurricane Katrina and Rita
during the summer of 2005. These
storm events may have further
exacerbated vegetated marsh losses
by creating open water pockets or
lakes to replace vegetated wetlands
in St. Bernard and Plaquemines
Parishes, Louisiana (USGS 2005b).
Estuarine emergent wetlands have
been restored elsewhere in the
country. An estimated 2,540 acres
were reclaimed from freshwater
wetlands through projects such as
the Dande Meadows Salt Marsh
Project in Massachusetts. This
project restored natural salt marsh
that had been converted into a
freshwater hayfield during colonial
times (Coastal America 2003). Small
to moderate scale projects have
been undertaken within the National
Estuarine Research Reserve System
as well. There, the focus has been on
restoring salt marsh and seagrass
beds where ecological functions have
declined (Kennish 2004).
Table 4. Contrasting different estimates of wetland loss in Louisiana.
Habitat Description Estimated Loss Rate
Normalized1 Loss
Rate (Hectares per
Year)
Source
Coastal marsh 50 acres/day 7,390 ha Moorman (2005)
Ducks Unlimited Southern Region
Coast and wetlands 25 sq. mi./yr 6,480 ha Louisiana State University (2005)
Wetlands of coastal
Louisiana
50 sq. mi./yr 12,960 ha Louisiana Geological Survey and EPA (1987)
Louisiana’s wetlands 75 sq. km/yr 7,500 ha Williams (1995)
USGS—Marine and Coastal Geology Program
Louisiana’s wetlands 16,000 to 25,000 acres/yr 6,480 to 10,120 ha National Marine Fisheries Service (www.nmfs.noaa.
gov/habitat)(2005)
Coastal land 25 to 35 sq. mi/yr 6,480 to 9,070 ha Tulane University (2004)
Marsh 40 sq. mi./yr 10,360 ha USGS, National Wetland Research Center (2005)
Estuarine and Marine
emergent wetland
5,500 acres/yr 2,240 ha This Study
1Scaled to 365 days and expressed as hectares.
Conversion factors:
Square mile = 640 acres
Hectare = 2.47 acres
Square kilometer = 247 acres
54
Estuarine Shrub
Wetlands
Among the most notable components
of the estuarine shrub wetland
category are mangrove swamps.
The geographic extent of mangroves
has been influenced by cold
temperatures, hurricanes, and
human induced stressors (Spalding
et al. 1997). Florida has always been
the primary location of mangrove
wetlands in the United States.
Mangrove species are uniquely
adapted to saline environments
and ecologically mangroves have
supported a diversity of wildlife
(Odum and McIvor 1990). Mangrove
communities and surrounding
waters of south Florida support
more than 220 species of fish, 24
species of reptiles and amphibians,
18 mammals and 181 bird species
(U.S. Fish and Wildlife Service 1996)
(Figure 36).
Mitsch and Gosselink (1993)
indicated that the northern-most
extent of black mangrove (Avicennia
geminans) occurred at about 30
degrees N. latitude. Although
scattered stands of mangrove shrubs
have been found along the north
coast of the Gulf of Mexico (Odum
and McIvor 1990), these wetlands
have been exposed to freezing
temperatures that greatly reduced
their number and distribution.
Estuarine shrub wetlands may have
included woody species other than
mangroves. Other salt-tolerant
or invasive woody plants in these
northern wetlands included false
willow (Baccharis angustifolia),
saltbush (Baccharis halimifolia),
buttonwood (Conocarpus erectus),
bay cedar (Suriana maritina)
and Brazilian pepper (Schinus
terebinthifolius).
There were an estimated 682,200
acres (276,190 ha) of estuarine shrub
wetland in 2004. This estimate
represented a gain of about 800
acres (320 ha). Most of this gain
came from areas formerly classified
as estuarine emergent wetland.
The acreage estimates of estuarine
shrub wetlands have been steady or
increased slightly over the past two
decades.
The long term trend in all intertidal
wetlands, estuarine vegetated and
estuarine non-vegetated categories
is shown in Figure 37 A-C. Estuarine
vegetated wetlands have continued
to decline over time as losses to the
estuarine emergent category have
overshadowed the small gains to
estuarine shrub wetlands.
Figure 36. Pelican Island, Florida, the nation’s first National Wildlife Refuge is located in the Indian River Lagoon, a
biologically diverse estuary of mangrove islands, salt marsh, and maritime hammocks. Photo courtesy of the FWS.
55
Figure37 A–C. Long-term trends in A) all intertidal wetlands, B) estuarine vegetated wetlands and C) estuarine non-vegetated
wetlands, 1950s to 2004.
56
5,000
5,200
5,400
5,600
5,800
6,000
6,200
Acres (in Thousands)
B. Estuarine Vegetated Wetlands
4,200
4,400
4,600
4,800
5,000
5,200
1950s 1970s 1980s 1998 2004
Acres (in Thousands)
C. Estuarine Non-vegetated Wetlands
0
200
400
600
800
1,000
1950s 1970s 1980s 1998 2004
Acres (in Thousands)
A. All Intertidal Wetlands
6,000
5,500
5,399
5,329
5,300
1950s 1970s 1980s 1998 2004
4,604
4,572
4,623
4,854
5,000
594 594 600
678
741
Wetland Values for Fish and Wildlife
Wetlands and Fish
Formed in 1922, The Izaak Walton League is one
of the nation’s oldest conservation organizations
to address deteriorating conditions of America’s top
fishing streams. The League is named for the 17th-century
English angler-conservationist who wrote the
literary classic “The Compleat Angler.” Since 1992,
the League has been restoring wetlands and streams,
establishing wildlife refuges and parks, and teaching
outdoor ethics to outdoor enthusiasts, sportsmen
and conservationists. League members recognize
the importance of wetlands and the role they play
in supporting fish species and angling opportunities
throughout the United States.
Fish and seafood provide the largest source of protein
for people across the world. The worldwide fish harvest
has surpassed cattle production and poultry farming
as the primary source of animal protein (FAO 1987).
The United States consumes more than 4 billion tons of
fish and shellfish every year—an average of 16 pounds
per person (National Marine Fisheries Service 2004).
Additionally, about 34 million people in the United
States fish for recreation (USFWS 2001).
America’s coastal and freshwater fish populations are
currently facing an unprecedented decline. Since 1900,
123 aquatic freshwater species have become extinct
in North America. Of the 822 native freshwater fish
species in the United States, 39 percent are at risk
of extinction (Fisheries and Water Resources Policy
Committee 2004) and 72 percent of freshwater mussels
are imperiled (USFWS 2004a). Additionally, the world’s
catch of ocean fish has been steadily falling since 1989,
with 13 of the 17 most productive fisheries currently
facing steep declines. Several factors have contributed
to this decline, including over-fishing and pollution.
However, the rate at which America’s fish populations
are plummeting is largely due to the loss and alteration
of their aquatic habitats.
At one time, the conterminous United States contained
more than 220 million acres of wetland habitat.
Although government programs, conservation
organizations, and private individuals are slowing
wetland loss and restoring degraded wetlands, the total
wetland acreage in the lower 48 states has declined to
the current 107 million acres. The nation’s wetlands are
vital to fish health. Wetlands provide an essential link
in the life cycle of 75 percent of the fish and shellfish
commercially harvested in the United States, and up
to 90 percent of the recreational fish catch. Wetlands
provide clean water, a consistent food supply, shelter,
and nursery areas for both marine and freshwater
species. Salmon, winter flounder, and largemouth bass,
among others, depend on healthy wetlands.
Largemouth bass (Micropterus salmoides) is the most popular game fish in the
United States. Shallow marshes at the edges of lakes and floodplain wetlands of
large, slow moving rivers are favorite habitats for the largemouth bass. Stocking
largemouth in smaller ponds and recreational lakes has been a common sport
fishery management practice in many states. Image courtesy of FWS.
57
By providing essential habitat and other benefits to fish
populations, wetlands play a crucial role in maintaining
the long-term health of our aquatic resources and
contribute to economic prosperity. Sport fishing is
responsible for a multi-million dollar industry that
supports television shows, magazines, fishing clubs
and organizations, tackle and boat manufacturing and
fishing tournaments held nationwide. In total, wetland-dependent
species make up 71 percent of the commercial
and recreational fisheries, supporting an industry that
contributes $111 billion annually to our national economy
and employs two million people (Fisheries and Water
Resources Policy Committee 2004).
How Wetlands Support Healthy Fish Populations
Clean Water
Wetlands have been termed “nature’s kidneys” because
they filter and purify our streams, rivers and waterways.
Wetlands slow down
moving water, allowing
sediments suspended in
the water to gradually
settle to the ground.
Cattails (Typha spp.)
and other ermergent and
submergent vegetation
help remove dangerous
heavy metals, like
copper and arsenic,
from the water column.
Other pollutants, like
lead, mercury and
pesticides, are trapped
by soil particles and are
gradually broken down
by microbes. Wetland
plants and microorganisms
also filter out and absorb
excess nutrients that
can result from fertilizer
application, manure, and
municipal sewage. When large amounts of nitrogen
and phosphorus enter our waterways, a massive
overgrowth of algae can occur, depleting dissolved
oxygen levels and stressing fish populations. Wetlands
can remove more than half of the phosphorous and 75
percent of the nitrogen out of the incoming water flow
(U.S. Environmental Protection Agency 1993) This
natural filtering ability reduces the negative impacts
of agricultural and municipal run-off, and it lessesns
the need to implement costly technological solutions.
For example, if half of all the existing wetlands were
destroyed, it would cost over $62 billion per year to
upgrade sewage treatment plants to handle all the extra
pollution (Environmental Defense Fund and World
Wildlife Fund 1992) Some types of wetlands are so good
at this filtration function that environmental managers
construct similar artificial wetlands to treat storm water
and wastewater near urban centers.
58
Sockeye salmon (Oncorhynchus nerka) spend their life in open sea, but return
to freshwater streams to spawn. These fish support one of the most important
commercial fisheries on the Pacific coast. Image courtesy of FWS.
Northern Pike (Esox lucius) and Muskellunge (Esox
masquinongy) are found in heavily vegetated wetlands
in the shallow waters along the edges of lakes and
large rivers. These are some of North America’s most
important freshwater game fish species. Image courtesy
of FWS.
Food Production
The diverse conditions found in wetlands allow
many different types of organisms, some with
highly specialized adaptations, to co-exist within a
small area. This wide range of species is supported
by the extraordinary rates of plant productivity
that characterize most wetland habitats. Some fish
species benefit directly by feeding on plant parts,
while other fish eat the small insects and crustaceans
that live on plants. Some fish prefer wetland plant
material that forms the detritus found on the bottom
of aquatic habitats. Wetlands indirectly nourish the
entire aquatic system when this rich organic matter is
washed downstream, where it benefits fish living many
miles away in the open ocean. Menhaden (Brevoortia
tyrannus), for example, rely upon detritus for a full
third of their diet, even though they live far from the
wetlands where it is produced.
Spawning and Nursery Areas
Fish eggs and young fish have different needs. Some fish
live in other habitats as adults and return to wetlands
to lay their eggs. Defenseless and immobile eggs can
be hidden from predators by underwater vegetation.
Wetland plants and detritus provide a surface for some
fish to attach their eggs. When the eggs hatch, the
vegetation becomes both a protective cover and a food
source. Young fish dart into the wetland vegetation to
hide, while the juvenile stages of bay scallops, hard
clams, and some other shellfish cling to salt marsh
vegetation and seagrasses for several weeks before
settling on the bottom. Most shrimp harvested in the
Gulf of Mexico depend on salt marshes for nurseries, yet
this latest study reports that these salt marsh wetlands
continued to decline by over 33,000 acres (13,450 ha)
between 1998 and 2004.
Refuge
Both adult and juvenile fish use wetlands to hide from
predators. Thick plant growth can visually confuse
predators and disguise small fish. Juvenile muskellunge,
northern pike and other and mottled colored fish can
hide by blending in with surrounding aquatic vegetation.
Dense vegetation and shallow water prevent many
pelagic predators from entering coastal marshes and
freshwater wetlands fringing lakes and rivers. Anchovies
(Engraulis mordax), juvenile snook (Centropomus
undecimalis), and juvenile spotted seatrout (Cynoscion
nebulosus) dart into the intertwining root systems of
mangrove wetlands to escape larger predators. The
root systems of trees and shrubs in floodplain wetlands
allow stream banks to hang over the water, providing
protective habitat for Chinook salmon (Oncorhynchus
tshawytscha), cutthroat trout (Oncorhynchus clarki),
and other fish.
Fish also use wetlands to seek refuge from changes in
water level, velocity, or bad weather. Coho salmon rely
on the calmer waters of forested wetlands adjacent to
streams to escape fast currents during winter floods.
Wetland plants help maintain appropriate levels of
oxygen in the water and keep temperatures cool for
aquatic life.
59
Rainbow trout, Onchorhynchus mykiss.
Image courtesy of FWS.
Black Crappie (Pomoxis nigromaculatus) and White Crappie (Pomoxis
annularis) use submerged vegetation and brush as spawning habitats. Image
courtesy of FWS.
Management and conservation for all aquatic resources
are a shared responsibility. Agencies, organizations and
individuals must continue to be involved in wetlands
and fisheries conservation activities to protect these
important resources.
Leah Miller and Suzanne Zanelli, Izaak
Walton League of America
www.iwla.org
Some of the information in this article was taken from the
publication Wetlands and Fish: Catch the Link, produced by
the Izaak Walton League and the National Marine Fisheries
Service. You can download this publication at http://www.
nmfs.noaa.gov/habitat/habitatconservation/publications/
hcpub.htm
6600
Brook trout, Salvelinus fontinalis
Image courtesy of FWS.
Photos courtesy of FWS.
Freshwater
Wetland
Resources
Freshwater, or palustrine, wetlands
included forested wetlands,
freshwater emergents, shrubs, and
freshwater ponds less than 20 acres
(8 ha). Freshwater wetlands have
been known by many common names
such as swamp, bog, fen, marsh,
swale, oxbow and wet meadow.
Ninety five percent of all wetland
area in the conterminous United
States was freshwater. In 2004, there
were an estimated 102.5 million
acres (41.5 million ha) of freshwater
wetlands. Table 5 summarized the
changes in freshwater wetlands
between 1998 and 2004.
Gains and Losses in Freshwater
Wetlands
There have been large shifts
between the freshwater wetland
types and uplands. Most wetland
loss (e.g. drainage, fills) and wetland
creation and restoration that
occurred between 1998 and 2004
involved some type of freshwater
wetland.
All net gains in wetland area took
place in freshwater systems. Overall,
the estimated net gain in freshwater
wetland area between 1998 and 2004
was 220,200 acres (89,140 ha).
Freshwater wetland gains resulted
from wetland restorations and the
creation of numerous freshwater
ponds (Figure 38). The status of
freshwater ponds is discussed later
in this section.
Wetland Restoration—Between
1987 and 1990, programs to restore
wetlands under the 1985 Food
Security Act added about 90,000
acres (36,400 ha) to the nation’s
wetland base (Dahl and Johnson
1991). Between 1986 and 1997, there
was a net gain of wetland from
“other” uplands of about 180,000
acres (72,900 ha) (Dahl, 2000).
During those previous study periods
wetland restoration and creation was
not sufficient to overcome wetland
losses. From 1986 to 1997, there was
a deficit between freshwater wetland
losses and gains of about 630,000
acres (255,100 ha). This was due to
freshwater wetland conversion to
upland land uses (Dahl 2000).
The federal government works
cooperatively with landowners,
states, tribes and communities
through a number of programs to
achieve restoration, protection and
improvement (see Appendix D). One
of the primary wetland restoration
programs of the Fish and Wildlife
Service is the Partners for Fish and
Wildlife Program. This program has
been available to private landowners
and has provided both technical
and financial assistance to restore
wetlands and other fish and wildlife
habitats. Examples of restoration
projects include restoring wetlands,
planting native trees and grasses,
removal of exotics, prescribed
burning, reconstruction of stream
habitat and reestablishment of fish
passageways (www.fws.gov/partners
2005).
Another restoration program of
the Fish and Wildlife Service is
the North American Waterfowl
Management Plan (NAWMP),
a public-private approach to
managing waterfowl populations.
Cooperation and coordination with
partners and stakeholders is key
to implementation of NAWMP
Table 5 Changes in freshwater wetland area between 1998 and 2004. The coefficient of variation (CV) for each entry
(expressed as a percentage) is given in parentheses.
Area, in Thousands of Acres
Freshwater Wetland Category Estimated Area,
1998
Estimated Area,
2004
Change,
1998–2004
Change
(in Percent)
Freshwater Emergent 26,289.6
(8.0)
26, 147.0
(8.0)
–142.6
*
–0.5
Freshwater Forested 51,483.1
(2.8)
52,031.4
(2.8)
548.2
(56.1)
1.1
Freshwater Shrub 18,542.2
(4.1)
17.641.4
(4.3)
–900.8
(34.2)
–4.9
Freshwater Vegetated Wetlands 96,314.9
(3.0)
95,819.8
(3.0)
–495.1
(35.0)
–0.5
Ponds1 5,534.3
(3.7)
6,229.6
(3.5)
695.4
(13.1)
12.6
Miscellaneous Types2 384.4
(16.3)
404.3
(15.6)
19.9
(54.2)
5.2
Freshwater Non-Vegetated 5,918.7
(3.7)
6,633.9
(3.5)
715.3
(12.8)
12.1
All Freshwater Wetlands 102,233.6
(2.9)
102,453.7
(2.8)
220.2
(77.3)
0.2
* Statistically unreliable.
1Includes the categories: Palustrine Aquatic Bed and Palustrine Unconsolidated Bottom.
2Palustrine Unconsolidated Shore.
Percent coefficient of variation was expressed as (standard deviation/mean) x (100).
61
Figure 38. Approximate density and distribution of freshwater wetland gains identified in the samples of this study.
Figure 39. A tile drained wetland basin has been restored. Ohio, 2005.
62
Wetland Gain
0–50 Acres
51–100 Acres
101–250 Acres
251–600 Acres
Figure 40. Wetland
restoration (freshwater
emergent) on land
previously classified as
upland “other.” Indiana,
2005. Photo by
M. Bergeson.
and to successfully protect and
conserve waterfowl through
habitat protection, restoration,
and enhancement. The habitat
objectives of NAWMP identify
key waterfowl habitat areas and
call for their conservation and
protection. Working with partners
and cooperators NAWMP seeks
to enhance, protect and restore
wetlands that contribute to those
waterfowl habitat objectives.
Over the past decade, many agencies
and organizations have been actively
involved in wetland restoration,
enhancement or creation. Many
beneficial projects have been
completed by federal, state, local
and private organizations and
citizens. Some of these projects
have involved removal of invasive
species in wetlands, restoration
of hydrology to partially drained
habitats, selective plantings and
reestablishment of vegetation,
improved wetland quality and other
habitat improvement activities.
These wetland enhancement
projects have not contributed area
gains to the wetland base and were
not part of this study.
An estimated 564,300 acres (228,460
ha) of wetlands were restored on
agricultural lands between 1998
and 2004. However, the loss of
wetlands to agricultural land use
was responsible for an estimated
488,200 acres (197,650 ha) during the
same period. The net gain of about
76,100 acres ( 30,800 ha) did not tell
the entire story of wetland restored
or created from agricultural
land. As lands became enrolled
in retirement or conservation
programs, they were subsequently
re-classified to the upland “other”
land use category (e.g. there were no
identifiable land use characteristics).
Thus, some areas attributed to
wetland restoration were actually
conversions of upland agricultural
land to the upland “other” category.
Replacement of wetland with a
structure (house or office building)
or development resulting from urban
or suburban infrastructure (roads
and bridges), usually constituted
an irreversible loss (Ainslie 2002).
It follows that most restoration and
creation of freshwater wetlands
would have to come from the
agricultural sector or undeveloped
lands classified as “other.” The
“other” lands category also included
many conservation lands such
as undeveloped land on National
Wildlife Refuges, in state game
management areas or preserves,
idle lands or land in retirement
programs planted to permanent
cover, as well as national and state
park lands (Figure 40). This trend
of gaining wetland acres from the
“other” land use category was seen
in the previous era study where
180,000 acres (72,900 ha) of “other”
land was converted to wetland (Dahl
2000).
63
The Council on Environmental
Quality (2005) provided an
assessment of wetland restoration
and creation by federal programs
that showed 58 percent of
the acreage was attributed to
agricultural conservation and
technical assistance programs and
about 32 percent was attributed
to other federal initiatives such as
those completed on conservation
lands.
The National Resources Inventory
conducted by the U.S. Department
of Agriculture estimated a total net
change of 263,000 acres (106,470
ha) in freshwater and estuarine
wetlands on nonfederal land from
Figure 41. Wetland restoration attributed to agricultural conservation programs in the upper midwest, 2004. The wetland can be
seen in the center with light green and white vegetation, darker irregular shape is surface water with vegetation.
1997 to 2003 (USDA—NRCS 2004).
Despite subtle differences and
nuances between that study and
this study and different timeframes,
there was general agreement
between the studies with regard to
wetland trends due to agriculture.
Agricultural conservation programs

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U.S. Fish & Wildlife Service
Status and Trends of
Wetlands in the Conterminous
United States 1998 to 2004
Inside front cover
Status and Trends of
Wetlands in the Conterminous
United States 1998 to 2004
T. E. Dahl
U.S. Fish and Wildlife Service
Fisheries and Habitat Conservation
Washington, D.C.
Opposite page: Louisiana, 2005.
Previous, title page: Freshwater wetland
in the southeast U.S., 2005.
Acknowledgments
Many agencies, organizations,
and individuals contributed their
time, energy, and expertise to the
completion of this report. The author
would like to specifically recognize
the following individuals for their
contributions. From the Fish and
Wildlife Service:
Dr. Benjamin Tuggle, John Cooper,
Herb Bergquist, Jim Dick, Jonathan
Hall , Bill Pearson, Becky Stanley ,
Dr. Mamie Parker, Everett Wilson,
Jill Parker, Robin Nims Elliott.
From the U.S. Geological Survey:
Greg Allord, Dave McCulloch, Mitch
Bergeson, Jane Harner,
Liz Ciganovich, Marta Anderson,
Dick Vraga, Tim Saultz, Mike
Duncan, Ron Keeler and the
staff of the Advanced Systems
Center. From the National Park
Service–Cumberland Island
National Seashore: Ginger Cox,
Ron Crawford and George Lewis.
From the Interagency Field Team:
Sally Benjamin, USDA–Farm
Services Agency; Patricia Delgado,
NOAA, National Marine Fisheries
Service; Dr. Jeff Goebel and Daryl
Lund, USDA–Natural Resources
Conservation Service; David Olsen,
U.S. Army Corps of Engineers; and
Myra Price, U.S. Environmental
Protection Agency.
Peer review of the manuscript was
provided by the following technical
experts: Ms. Peg Bostwick, Michigan
Dept. of Environmental Quality,
Lansing, MI; Dr. Ken Burham,
Statistician, Department of Fishery
and Wildlife Biology, Colorado State
University, Fort Collins, CO; Mr.
Retired.
Current affiliation: NOAA, National Marine
Fisheries Service.
Marvin Hubbell, U.S. Army Corps of
Engineers, Rock Island, IL;
Mr. William Knapp, Deputy Science
Advisor, U.S. Fish and Wildlife
Service, Arlington, VA; Ms. Janet
Morlan, Oregon Dept. of State Lands,
Salem, OR; Dr. N. Scott Urquhart
Research Scientist, Department of
Statistics, Colorado State University,
Fort Collins, CO; Mr. Joel Wagner,
Hydrologist, National Park Service,
Denver, CO; Dr. Dennis Whigham,
Senior Scientist, Smithsonian
Environmental Research Center,
Edgewater, MD; Dr. Joy Zedler,
Professor of Botany and Aldo
Leopold Chair in Restoration
Ecology, University of Wisconsin,
Madison, WI.
This report is the culmination
of technical collaboration and
partnerships. A more complete listing
of some of the cooperators appears at
the end of this report.
Publication design and layout of the
report were done by the Cartography
and Publishing Program, U.S.
Geological Survey, Madison,
Wisconsin.
Photographs are by Thomas Dahl
unless otherwise noted.
This report should be cited as follows:
Dahl, T.E. 2006. Status and trends
of wetlands in the conterminous
United States 1998 to 2004.
U.S. Department of the Interior;
Fish and Wildlife Service,
Washington, D.C. 112 pp.
Tundra swans (Cygnus columbianus) and other waterfowl congregate in the freshwater marshes along
the upper Mississippi River. Photo courtesy of FWS.
Funding for this study was
provided by the following
agencies:
Environmental Protection Agency
Department of Agriculture
Farm Services Administration
Natural Resources Conservation Service
Department of Commerce
National Marine Fisheries Service
Department of the Army
Army Corps of Engineers
Department of Interior
Fish and Wildlife Service
The Council of Environmental Quality has
coordinated these interagency efforts.
A freshwater emergent wetland in Nebraska, 2005.
Preface
Secretary, Department of the Interior
On Earth Day 2004, President Bush
unveiled a new policy for our nation’s
wetlands. Moving beyond “no net
loss” of wetlands, the President
challenged the nation to increase the
quantity as well as quality of these
important resources, and set a goal
of restoring, improving and
protecting more than 3 million
acres in five years.
The President recognized that a
continuous effort to track progress
toward achieving the various aspects
of the Administration’s new policies
would be important. The Fish and
Wildlife Service was in a unique
position to provide the nation with
sound scientific information
assessing trends in the quantity of
wetland gains and losses. As part of
that same 2004 Earth Day message,
the President directed the Service
to accelerate the completion of this
study and report the results.
This is the Administration’s report
to Congress that provides the nation
with scientific and statistical results
on progress made toward our
national wetlands acreage goals.
I am pleased to report that the
nation is making excellent progress
in meeting these wetland goals. For
the first time net wetland gains,
achieved through the contributions
of restoration and creation activities,
surpassed net wetland losses.
This is the result of a multitude of
governmental, corporate and private
partnerships working together to
secure and conserve our wetland
resources for future generations.
This report does not draw
conclusions regarding trends in
the quality of the nation’s wetlands.
The Status and Trends Study collects
data on wetland acreage gains and
losses, as it has for the past 50 years.
However, it is timely to examine
the quality, function, and condition
of such wetland acreage. Such an
examination will be undertaken
by agencies participating in the
President’s Wetlands Initiative.
U.S. Customary to Metric
inches (in.) x 25.40 = millimeters (mm)
inches (in.) x 2.54 = centimeters (cm)
feet (ft) x 0.30 = meters (m)
miles (mi) x 1.61 = kilometers (km)
nautical miles (nmi) x 1.85 = kilometers (km)
square feet (ft2) x 0.09 = square meters (m2)
square miles (mi2) x 2.59 = square kilometers (km2)
acres (A) x 0.40 = hectares (ha)
Fahrenheit degrees (F) → 0.56 (F - 32) = Celsius degrees (C)
Metric to U.S. Customary
millimeters (mm) x 0.04 = inches (in.)
centimeters (cm) x 0.39 = feet (ft)
meters (m) x 3.28 = feet (ft)
kilometers (km) x 0.62 = miles (mi)
square meters (m2) x 10.76 = square feet (ft2)
square kilometers (km2) x 0.39 = square miles (mi2)
hectares (ha) x 2.47 = acres (A)
Celsius degrees (C) → 1.8 (C) + 32) = Fahrenheit degrees (F)
General Disclaimer
Conversion Table
The use of trade, product, industry or firm names or products in this report is for informative
purposes only and does not constitute an endorsement by the U.S. Government or the Fish and
Wildlife Service.
Contents
Preface......................................................................................................................................................................... 7
Executive Summary.................................................................................................................................................15
Introduction.............................................................................................................................................................. 19
Study Design and Procedures................................................................................................................................21
Study Objectives................................................................................................................................................21
Sampling Design................................................................................................................................................ 24
Types and Dates of Imagery............................................................................................................................26
Technological Advances....................................................................................................................................30
Methods of Data Collection and Image Analysis...........................................................................................30
Wetland Change Detection............................................................................................................................... 31
Field Verification................................................................................................................................................ 3
Quality Control................................................................................................................................................... 34
Statistical Analysis............................................................................................................................................36
Limitations.......................................................................................................................................................... 37
Attribution of Wetland Losses.........................................................................................................................39
Results and Discussion............................................................................................................................................43
Status of the Nation’s Wetlands.......................................................................................................................43
Attribution of Wetland Gain and Loss.............................................................................................................47
Intertidal Estuarine and Marine Wetland Resources...................................................................................48
Marine and Estuarine Beaches, Tidal Bars, Flats and Shoals.....................................................................50
Estuarine Emergent Wetlands........................................................................................................................52
Estuarine Shrub Wetlands...............................................................................................................................5
Wetland Values for Fish and Wildlife–insert–Wetlands and Fish...............................................................57
Freshwater Wetland Resources.......................................................................................................................61
Freshwater Lakes and Reservoirs...................................................................................................................78
Terminology and Tracking Wetland Gains......................................................................................................78
Wetland Restoration and Creation on Conservation Lands................................................................................81
Wetland Restoration–insert–Restoration on the Upper Mississippi River.........................................82
Wetland Restoration–insert–Restoring Iowa’s Prairie Marshes..........................................................85
Monitoring Wetland Quantity and Quality­—
Beyond No-Net-Loss............................................................89
Minnesota’s Comprehensive Wetland Assessment and Monitoring Strategy....................................90
Summary................................................................................................................................................................... 93
References Cited...................................................................................................................................................... 95
Acknowledgement of Cooperators.........................................................................................................................98
Appendix A: Definitoins of habitat categories used in this study.....................................................................101
Appendix B: Hammond (1970) physiographic regions of the United States...................................................105
Appendix C: Wetland change from 1998 to 2004.................................................................................................106
Appendix D: Representative Wetland Restoration Programs and Activities.................................................109
10
List of Figures
Figure 1. A cypress (Taxodium distichum) wetland near the White River, Arkansas, 2005.........................19
Figure 2. A gallery of wetland images....................................................................................................................20
Figure 3. Open water lakes, such as this reservoir were classified as deepwater habitats
if they exceeded 20 acres (8 ha). Piney Run Lake, Maryland, 2005...................................................................2
Figure 4. Coastal wetlands offshore from the mainland include salt marsh
(estuarine emergent) (A), shoals (B), tidal flats (C) and bars.............................................................................24
Figure 5. Physiographic subdivisions of North Carolina and sample plot distribution as used
in this study...............................................................................................................................................................25
Figure 6. High resolution, infrared Ikonos satellite image of bogs (A), lakes (B) and wetlands (C)
of northern Wisconsin, spring 2005........................................................................................................................26
Figure 7. Early spring 2005 Ikonos satellite image of Michigan. Leaf-off condition
made recognition of wetland features easier.........................................................................................................27
Figure 8. Mean date of imagery used by state......................................................................................................28
Figure 9. True color NAIP photographs scale show farmland (A), forest (B), wetlands (C)
and lakes (D) in Indiana, 2003................................................................................................................................29
Figure 10. A small wetland basin estimated to have been about seven square meters...................................30
Figure 1. Change detection involved a comparison of plots at two different times (T1 and T2)..................31
Figure 12. A true color aerial photograph shows a new drainage network
(indicated by red arrow) and provides visual evidence of wetland loss.............................................................32
Figure 13. Lands in transition from one land use category to another pose unique challenges
for image analysts....................................................................................................................................................32
Figure 14. Field verification was completed at sites in the 35 states as shown on the map............................3
Figure 15. Topographic maps in digital raster graphics format were used as auxillary
information and for quality control........................................................................................................................35
Figure 16. Digital wetlands status and trends data were viewed combined with contemporary
georeferenced color infrared imagery of the study areas....................................................................................35
Figure 17. The Pacific coastline..............................................................................................................................37
Figure 18 A and B. Commercial rice fields where water was pumped to flood the rice crop.........................38
Figure 19 A and B. Examples of agricultural land use........................................................................................39
Figure 20. Trees planted in rows with uniform crown height (A) and block clear cuts [blue-green
feature in center (B)] were indicators of managed forest plantations..............................................................40
Figure 21. Urban wetlands (shown as dark blue-black) outside of a shopping mall are
surrounded by high density urban development. New Jersey, 2003, color infrared photograph...................41
Figure 2. Wetland area compared to the total land area of the conterminous United States, 2004............43
Figure 23. Salt marsh along the Ecofina River, Florida .....................................................................................45
Figure 24. Percentage of estimated estuarine and freshwater wetland area and covertypes, 2004..............45
Figure 25. A freshwater wetland in the southeastern United States 2005........................................................46
Figure 26. Average annual net loss and gain estimates for the conterminous
United States, 1954 to 2004.....................................................................................................................................46
11
Figure 27. Wetlands gained or lost from upland categories and deepwater, 1998 to 2004..............................47
Figure 28. Composition of marine and estuarine intertidal wetlands, 2004......................................................48
Figure 29. Estimated percent loss of intertidal estuarine and marine wetlands to
deepwater and development, 1998 to 2004.............................................................................................................49
Figure 30. Non-vegetated tidal flats grade into sparsely vegetated beach ridges. These areas
are important for a variety of birds, sea turtles and other marine life..............................................................50
Figure 31. Intertidal marine beaches provide important habitat for shorebirds.............................................51
Figure 32. The black necked stilt (Himantopus mexicanus) inhabits mud flats, pools,
back water beaches and brackish ponds of saltwater marshes among other wetland habitats......................51
Figure 3. New shoals and sand bars are continually forming in shallow water areas.
This image shows a new feature (brightest white areas) off the coast of Virginia, 2004.................................51
Figure 34. High altitude infrared photograph of salt marsh (darker mottles), coastal Georgia, 2004..........52
Figure 35. Estuarine emergent losses as observed in this study along the Atlantic and Gulf of Mexico.
Inset shows close up of Louisiana where most losses occurred between 1998 and 2004.................................53
Figure 36. Pelican Island, Florida, the nation’s first National Wildlife Refuge is located in
the Indian River Lagoon, a biologically diverse estuary of mangrove islands, salt marsh,
and maritime hammocks.........................................................................................................................................5
Figure 37 A–C. Long-term trends in A) all intertidal wetlands, B) estuarine vegetated wetlands and
C) estuarine non-vegetated wetlands, 1950s to 2004............................................................................................56
Figure 38. Approximate density and distribution of freshwater wetland acreage gains indentified
in the samples of this study.....................................................................................................................................62
Figure 39. A tile drained wetland basin has been restored. Ohio, 2005.............................................................62
Figure 40. Wetland restoration (freshwater emergent) on land previously classified
as upland “other.”.....................................................................................................................................................63
Figure 41. Wetland restoration attributed to agricultural conservation programs in the
upper midwest, 2004................................................................................................................................................64
Figure 42. A restored wetland basin.......................................................................................................................65
Figure 43 A and B. Private efforts to restore wetlands also contributed to the national acreage
base in this study. A) western Minnesota, 2004; B) Stone Lake,
Wisconsin, 2005.........................................................................................................................................................65
Figure 4. Example of wetland loss. Fill being placed into a wetland pond in Ohio, 2005..............................6
Figure 45. An emergent wetland in rural Pennsylvania, 2005, in the process of being filled.
Both examples in Figures 46 and 47 were attributed to Rural Development...................................................6
Figure 46. Areas experiencing wetland loss due to development, 1998 to 2004...............................................67
Figure 47. Development in rapidly growing area of south Florida....................................................................68
Figure 48. Trends in the estimated annual loss rate of freshwater vegetated
wetland area, 1974 to 2004......................................................................................................................................69
Figure 49. A mitigation banking site. As wetlands were converted elsewhere, cells of the
mitigation bank were flooded to create replacement wetland. 2004..................................................................69
Figure 50. Estimated percent loss of forested wetlands to the various upland land use
categories between 1998 and 2004..........................................................................................................................70
Figure 51. Forested wetland. Alabama, 2005. Photo courtesy of South Dakota State University.................70
Figure 52. A freshwater wetland dominated by the woody shrub False Indigo (Amorpha fruticosa).........71
Figure 53. Long-term trends in freshwater forested and shrub wetlands, 1950s to 2004..............................71
Opposite page: Freshwater wetlands of the Yosemite Valley, California.
12
Figure 54. This field has been squared off by agricultural drainage (surface ditch indicated
with red arrow). New Jersey, 2003..........................................................................................................................72
Figure 5. Subtle wetland drainage practices in the prairie pothole region of South Dakota........................73
Figure 56. Long-term trends in freshwater emergent wetlands, 1954 to 2004................................................73
Figure 57. A freshwater pond in central Kansas is starting to support emergent vegetation, 2005.............74
Figure 58. Number and approximate location of new freshwater ponds
created between 1998 and 2004..............................................................................................................................75
Figure 59. A newly created open water pond as part of a golf course. Maryland, 2005..................................75
Figure 62 A–D. Different ponds have been constructed for different purposes throughout
the United States......................................................................................................................................................76
Figure 61. Color infrared aerial photograph of new development in south Florida. Ponds and small
residential lakes (shown as dark blue) are surrounded by new housing...........................................................7
Figure 62. Commercial cranberry operations had created several
open water ponds (dark blue areas)........................................................................................................................7
Figure 63. Long-term trends in freshwater pond acreage, 1954 to 2004...........................................................7
Figure 64A and B. Freshwater lakes provide wildlife and fish habitat as well as opportunities for
recreation and education.........................................................................................................................................78
Figure 65. Created wetland on an area that was upland (dry land)...................................................................79
Figure 6. A wetland restoration (reestablishment). This former wetland basin had been completely
drained and reclassified as upland.........................................................................................................................79
Figure 67. “Improved” wetland or wetland enhancement—hydrology has been restored to
an existing albeit degraded wetland.......................................................................................................................79
Figure 68 . Wetland protection or preservation—included pre-existing wetland acres either
owned or leased long-term by a federal agency....................................................................................................79
Figure 69. A system of federal lands including National Wildlife Refuges and
Wetland Management Districts are restoring and enhancing wetland acres...................................................81
Table 1. Wetland, deepwater, and upland categories used to conduct
wetland status and trends studies..........................................................................................................................23
Table 2. Change in wetland area for selected wetland and deepwater categories, 1998 to 2004 ...................4
Table 3. Changes to estuarine and marine wetlands, 1998 to 2004.....................................................................49
Table 4. Contrasting different estimates of wetland loss in Louisiana..............................................................54
Table 5. Changes in freshwater wetland area between 1998 and 2004..............................................................61
Table 6. Contrasting the Fish and Wildlife Service’s Wetlands Status and Trends with the Council on
Environmental Quality report (2005) on federal efforts to track wetland gains..............................................80
List of Tables
13
14
Executive Summary
The first statistical wetlands status
and trends report (Frayer et al.
1983) estimated the rate of wetland
loss between the mid 1950s and the
mid 1970s at 458,000 acres (185,400
ha) per year. There have been
dramatic changes since that era
when wetlands were largely thought
of as a hindrance to development.
The first indications of those
changes came from the Fish and
Wildlife Service’s updated status
and trends report (Dahl and Johnson
1991) covering the mid 1970s to the
mid 1980s. The estimated rate of
wetland loss had declined to 290,000
acres (117,400 ha) per year.
In 2000, the Fish and Wildlife
Service produced the third
national status and trends report
documenting changes that occurred
between 1986 and 1997. Findings
from that report indicated the
annual loss rate was 58,500 acres
(23,700 ha), an eighty percent
reduction in the average annual rate
of wetland loss.
On Earth Day 2004, President Bush
announced a wetlands initiative that
established a federal policy beyond
“no net loss” of wetlands. The policy
seeks to attain an overall increase
in the quality and quantity of
wetlands. The President set a goal of
restoring, improving and protecting
more than 3 million acres (1.2
million ha) in five years. To continue
tracking wetland acreage trends, the
President further directed the Fish
and Wildlife Service to complete
an updated wetlands status and
trends study in 2005. This latest
report provides the nation with
scientific and statistical results on
the progress that has been made
toward achieving national wetland
quantity goals. This report does not
assess the quality or condition of
the nation’s wetlands. The Status
and Trends Study collects data on
wetland acreage gains and losses,
For over half a century the Fish
and Wildlife Service has been
monitoring wetland trends of the
nation. In 1956, the first report on
wetland status and classification
provided indications that wetland
habitat for migratory waterfowl had
experienced substantial declines
(Shaw and Fredine 1956).
Over the intervening 51 years,
the Fish and Wildlife Service has
implemented a scientifically based
process to periodically measure
wetland status and trends in the
conterminous United States. The
Fish and Wildlife Service’s Wetlands
Status and Trends study was
developed specifically for monitoring
the nation’s wetland area using a
single, consistent definition and
study protocol. The Fish and Wildlife
Service has specialized knowledge
of wetland habitats, classification,
and ecological changes and has used
that capability to conduct a series
of wetland monitoring studies that
document the status and trends of
our nation’s wetlands. This report is
the latest in that series of scientific
studies.
Data collected for the 1998 to 2004
Status and Trends Report has led to
the conclusion that for the first time
net wetland gains, acquired through
the contributions of restoration and
creation activities, surpassed net
wetland losses. There was a net gain
of 191,750 wetland acres (77,630
ha) nationwide which equates to an
average annual net gain of 32,000
acres (12,900 ha).
The efforts to monitor wetland
status and trends that are described
in this report have been enhanced
by the multi-agency involvement in
the study’s design, data collection,
verification, and peer review of the
findings. Interagency funding was
essential to the successful and timely
completion of the study.
A freshwater forested wetland of the
Great Lakes region, 2005.
15
as it has for the past 50 years.
However, it is timely to examine
the quality, function, and condition
of such wetland acreage. Such an
examination will be undertaken
by agencies participating in the
President’s Wetlands Initiative.
This study measured wetland
trends in the conterminous United
States between 1998 and 2004. The
estimates of estuarine emergent
area were made prior to Hurricanes
Katrina and Rita during the summer
of 2005. The Cowardin et al. (1979)
wetland definition was used to
describe wetland types. By design,
intertidal wetlands of the Pacific
coast, reefs and submerged aquatic
vegetation were excluded from this
study.
An interagency group of statisticians
developed the design for the national
status and trends study. The study
design consisted of 4,682 randomly
selected sample plots. Each plot is
four square miles (2,560 acres or
1,040 ha) in area. These plots were
examined, with the use of recent
remotely sensed data in combination
with field work, to determine
wetland change. Field verification
was completed for 1,504 (32 percent)
of the sample plots distributed in 35
states. Representatives from four
states and seven federal agencies
participated in field reconnaissance
trips.
Estimates were made of wetland
area by wetland type and changes
over time.
National Status
and Trends
This study found that there were
an estimated 107.7 million acres
(43.6 million ha) of wetlands in the
conterminous United States in 2004.
Ninety-five percent of the wetlands
were freshwater wetlands and five
percent were estuarine or marine
wetlands.
In the estuarine system, estuarine
emergents dominated, making up
an estimated 73 percent (almost 3.9
million acres or 1.6 million ha) of
all estuarine and marine wetlands.
Estuarine shrub wetlands made
up 13 percent of the area and non-vegetated
saltwater wetlands 14
percent.
In the freshwater system, forested
wetlands made up 51 percent of
the total area, the single largest
freshwater category. Freshwater
emergents made up an estimated
25.5 percent of the total area, shrub
wetlands 17 percent and freshwater
ponds 6.5 percent.
Wetland area increased by an
average 32,000 acres (12,900
ha.) annually. The net gain in
wetland area was attributed to
wetlands created, enhanced or
restored through regulatory
and nonregulatory restoration
programs. These gains in wetland
area occurred on active agricultural
lands, inactive agricultural lands,
and other lands. Freshwater wetland
losses to silviculture, urban and
rural development offset some
gains. Urban and rural development
combined accounted for an
estimated 61 percent of the net
freshwater wetlands lost between
1998 and 2004. This study reports
on changes in wetland acreage and
does not provide an assessment of
wetland functions or quality.
Intertidal
Estuarine and
Marine Wetland
Resources
Three major categories of estuarine
and marine wetlands were included
in this study: estuarine intertidal
emergents (salt and brackish water
marshes), estuarine shrub wetlands
(mangrove swamps) and estuarine
and marine intertidal non-vegetated
wetlands. This latter category
included exposed coastal beaches
subject to tidal flooding, shallow
water sand bars, tidal flats, tidally
exposed shoals, and sand spits.
In 2004, it was estimated there
were slightly more than 5.3
million acres (2.15 million ha) of
marine and estuarine wetlands in
the conterminous United States.
Estuarine emergent wetlands
declined by 0.9 percent. The average
annual rate of estuarine emergent
loss was 5,540 acres (2,240 ha). This
rate of loss was consistent with the
rate of salt marsh loss recorded from
1986 to 1997. Most of the losses of
estuarine emergent wetland were
due to loss to deep salt water and
occurred in coastal Louisiana. One
or more of several interrelated
factors may have contributed to
these losses including: deficiencies
in sediment deposition, canals and
artificially created waterways,
wave erosion, land subsidence, and
salt water intrusion causing marsh
disintegration.
There were an estimated 728,540
acres (294,960 ha) of intertidal
non-vegetated wetlands in 2004.
From 1998 to 2004 marine intertidal
beaches declined by 1,870 acres
(760 ha). Intertidal non-vegetated
wetland changes to urban and other
forms of upland development were
statistically insignificant in this
study.
There were an estimated 682,200
acres (276,190 ha) of estuarine shrub
wetland in 2004. This estimate
represented a small gain of about 800
acres (320 ha). The area of estuarine
shrub wetlands has been steady over
the past two decades.
Freshwater
Wetland
Resources
Large shifts between the freshwater
wetland types and uplands took
place between 1998 and 2004.
Freshwater wetland gains resulted
from restorations and the creation of
numerous freshwater ponds.
Agricultural conservation programs
were responsible for most of
the gross wetland restoration.
These gains came from lands in
“agriculture” category as well
as from conservation lands in
16
the “other” land use category.
Agricultural programs that
promoted pond construction
also contributed to the increased
freshwater pond acreage.
Ponds were included as freshwater
wetlands consistent with the
Cowardin et al. definition.
Freshwater pond acreage increased
by almost 700,000 acres (281,500 ha)
from 1998 to 2004, a 12.6 percent
increase in area. This was the
largest percent increase in area,
of any wetland type in this study.
Without the increased pond acreage,
wetland gains would not have
surpassed wetland losses during the
timeframe of this study. The creation
of artificial freshwater ponds has
played a major role in achieving
wetland quantity objectives.
The replacement of vegetated
wetland areas with ponds represents
a change in wetland classification.
Some freshwater ponds would not be
expected to provide the same range
of wetland values and functions as a
vegetated freshwater wetland.
Freshwater forested wetlands
were affected by two processes,
the conversion of forested wetland
to and from other wetland types
through cutting or the maturation of
trees, and loss of forested wetland
where wetland hydrology was
destroyed. Estimates indicated
that the area of freshwater forested
wetland increased. Between 1998
and 2004, forested wetland area
increased by an estimated 548,200
acres (221,950 ha). Most of these
changes came from small trees,
previously classified as wetland
shrubs, maturing and being re-classified
as forest.
Despite the net gains realized from
restoration and creation projects,
human induced wetland losses
continued to affect the trends of
freshwater vegetated wetlands—
especially freshwater emergent
marshes which declined by an
estimated 142,570 acres (57,720
ha). These wetlands are important
to a number of wildlife species.
Contributed inserts to the report
highlight the importance of wetlands
to fish and wildlife.
American avocets (Recurvirostra americana) at Bear River, Migratory Bird Refuge, Utah, a river delta wetland that attracts
hundreds of species of waterfowl and shorebirds. Photo courtesy of the FWS.
17
18
Introduction The mission of the Fish and Wildlife
Service is to conserve, protect, and
enhance fish, wildlife, plants, and
their habitats for the continuing
benefit of the American people. The
Fish and Wildlife Service supports
programs relating to migratory
birds, endangered species, certain
marine mammals, inland sport
fisheries and a system of 545
national wildlife refuges. The Fish
and Wildlife Service communicates
information essential for public
awareness and understanding
of the importance of fish and
wildlife resources and changes in
environmental conditions that can
affect the welfare of Americans.
To this end, the Fish and Wildlife
Service maintains an active role in
monitoring wetland habitats of the
nation.
The importance of wetlands as fish
and wildlife habitat has always been
the primary focus of the Fish and
Wildlife Service’s wetland activities.
Wetlands are transitional from truly
aquatic habitats to upland and as a
result, wetland abundance, type and
quality are directly reflected in the
health and abundance of many fish
and wildlife species.
The Emergency Wetlands Resources
Act (Public Law 99-645) requires
the Fish and Wildlife Service to
produce national wetlands status
and trend reports for the Congress
at ten year intervals. The Fish and
Wildlife Service has responded to
this mandate with national wetlands
status and trends reports in 1983,
1991 and 2000 (Frayer et al. 1983;
Tiner 1984; Dahl and Johnson 1991;
and Dahl 2000).
These wetland status and trend
reports have been used by federal,
state, local and tribal governments
to develop wetland conservation
strategies, measure the efficacy
of existing policies, and validate
comprehensive performance
toward halting loss and regaining
wetlands. Industry, the scientific
community, conservation groups,
decision makers and the public value
this contemporary information for
planning, decision-making, and on-the-
ground management.
Our nation’s wetlands goals have
historically been based on wetland
acreage and the ability to provide a
quantitative measure of the extent
of wetland area as a means to
measure progress toward achieving
the national goal of “no net loss.”
This concept was first formulated
as a national goal by the National
Wetlands Policy Forum (The
Conservation Foundation 1988)
and was later adopted as federal
policy by President George H.W.
Bush. In an effort to monitor the
status and trends in the quantity
and type of our nation’s wetlands, a
series of Fish and Wildlife Service
reports have documented a steadily
declining wetland loss rate. From
the mid 1950s to the mid 1970s, the
nation lost about 458,000 wetland
acres annually. This rate of loss
was substantially reduced to about
59,000 acres annually by 1997.
On Earth Day 2004, President
George W. Bush announced a
wetlands initiative that established a
federal policy beyond “no net loss” of
wetlands. The policy seeks to attain
an overall increase in the quality
and quantity of wetlands and set
a goal of restoring, improving and
protecting more than 3 million acres
(1.2 million ha) in five years (Council
on Environmental Quality 2005). To
continue tracking wetland trends,
the President further directed
the Fish and Wildlife Service to
complete an updated wetlands status
and trends study in 2005—five years
ahead of the mandated legislative
schedule.
This updated report used the
latest technologies in remote
sensing, geospatial analysis and
computerized mapping. The most
recent aerial and satellite imagery
available was analyzed to document
wetland change on 4,682 two-mile
square (5.2 sq. km) sample plots
located throughout the 48 states. It
covers the period from 1998 to 2004,
and provides the most recent and
comprehensive quantitative measure
of the areal extent of all wetlands
in the conterminous United States
regardless of ownership. The study
provides no qualitative assessments
of wetland functions.
Figure 1. A cypress (Taxodium
distichum) wetland near the White
River, Arkansas, 2005.
19
20
Study Objectives
This study was designed to provide
the nation with current, scientifically
valid information on the status
and extent of wetland resources
regardless of ownership and to
measure change in those resources
over time.
Wetland Definition and Classification
The Fish and Wildlife Service
used the Cowardin et al. (1979)
definition of wetland. This definition
is the standard for the agency
and is the national standard for
wetland mapping, monitoring
and data reporting as determined
by the Federal Geographic Data
Committee. It is a two-part
definition as indicated below:
Ephemeral waters, which are not
recognized as a wetland type, and
certain types of “farmed wetlands”
as defined by the Food Security
Act were not included in this
study because they do not meet
the Cowardin et al. definition.
The definition and classification of
wetland types have been consistent
in every status and trends study
conducted by the Fish and Wildlife
Service. Habitat category definitions
are given in synoptic form in Table
1. The reader is encouraged to also
review Appendix A, which provides
complete definitions of wetland
types and land use categories used
in this study.
Wetlands are lands transitional between terrestrial and aquatic
systems where the water table is usually at or near the surface
or the land is covered by shallow water.
For purposes of this classification wetlands must have one or
more of the following three attributes: (1) at least periodically,
the land supports predominantly hydrophytes, (2) the substrate
is predominantly undrained hydric soil, and (3) the substrate is
nonsoil and is saturated with water or covered by shallow water
at some time during the growing season of each year.
Study Design and Procedures
Figure 2. A gallery of wetland images. From top to bottom left; emergent marsh in Wisconsin, black-crowned night heron
(Nycticorax nycticorax) (FWS), shrub wetland in Michigan (courtesy of St. Mary’s University), Bosque del Apache National
Wildlife Refuge, New Mexico (FWS). From top to bottom right; forested wetland (FWS), Parker River National Wildlife
Refuge, Massachusetts (FWS), freshwater wetland, northern Indiana, 2005, American toad (Bufo americanus) (Isaac
Chellman, USGS).
21
Deepwater Habitats
Wetlands and deepwater habitats are
defined separately by Cowardin et
al. (1979) because the term wetland
does not include deep, permanent
water bodies. Deepwater habitats
are permanently flooded land lying
below the deepwater boundary of
wetlands (Figure 3). Deepwater
habitats include environments where
surface water is permanent and
often deep, so that water, rather
than air, is the principal medium in
which the dominant organisms live,
whether or not they are attached to
the substrate. For the purposes of
conducting status and trends work,
all lacustrine (lake) and riverine
(river) waters were considered
deepwater habitats.
Upland Habitats
An abbreviated upland classification
system patterned after the U. S.
Geological Survey land classification
scheme described by Anderson
et al. (1976), with five generalized
categories, was used to describe
uplands in this study. These
categories are listed in Table 1.
Figure 3. Open water lakes, such as this
reservoir were classified as deepwater
habitats if they exceeded 20 acres (8 ha).
Piney Run Lake, Maryland, 2005.
22
Table 1. Wetland, deepwater, and upland categories used to conduct wetland status and trends studies.
The definitions for each category appear in Appendix A.
Category Common Description
Salt Water Habitats
Marine Subtidal* Open ocean
Marine Intertidal Near shore
Estuarine Subtidal* Open-water/bay bottoms
Estuarine Intertidal Emergents Salt marsh
Estuarine Intertidal Forested/Shrub Mangroves or other estuarine shrubs
Estuarine Unconsolidated Shore Beaches/bars
Estuarine Aquatic Bed Submerged or floating estuarine vegetation
Riverine* (may be tidal or nontidal) River systems
Freshwater Habitats
Palustrine Forested Forested swamps
Palustrine Shrub Shrub wetlands
Palustrine Emergents Inland marshes/wet meadows
Palustrine Unconsolidated Shore Shore beaches/bars
Palustrine Unconsolidated Bottom Open-water ponds
Palustrine Aquatic Bed Floating aquatic/submerged vegetations
Palustrine Farmed Farmed wetland
Lacustrine* Lakes and reservoirs
Uplands
Agriculture Cropland, pasture, managed rangeland
Urban Cities and incorporated developments
Forested Plantations Planted or intensively managed forests, silviculture
Rural Development Non-urban developed areas and infrastructure
Other Uplands (see further explanation in Appendix A) Rural uplands not in any other category; barren lands
*Deepwater habitat
23
Sampling Design
This study measured wetland extent
and change using a statistically
stratified, simple random sampling
design, the foundations of which
are well documented (Dahl 2000;
USFWS 2004b). The sampling
design used for this study was
developed by an interagency
group of spatial sampling experts
specifically to monitor wetland
change. It can be used to monitor
conversions between ecologically
different wetland types, as well as
measure wetland gains and losses.
Sample plots were examined, with
the use of remotely sensed data
in combination with field work,
to determine wetland change.
To monitor changes in wetland
area, the 48 conterminous states
were stratified or divided by state
boundaries and 35 physiographical
subdivisions described by Hammond
(1970) (Appendix B).
Monitoring Wetlands
Stratification of the nation based on
differences in wetland density makes
this study an effective measure of
wetland resources. Some natural
resource assessments stop at county
boundaries or at a point coinciding
with the census line for inhabitable
land area. Doing so may exclude
offshore wetlands, shallow water
embayments or sounds, shoals, sand
bars, tidal flats and reefs (Figure
4). These are important fish and
wildlife habitats.
The Fish and Wildlife Service
included wetlands in coastal areas
by adding a supplemental sampling
stratum along the Atlantic and
Gulf coastal fringes. This stratum
includes the near shore areas of the
coast with its barrier islands, coastal
marshes, exposed tidal flats and
other offshore features not a part of
the landward physiographic zones.
The coastal zone stratum, included
28.2 million acres (11.4 million ha).
At its widest point in southern
Louisiana, this zone extended about
92.6 miles (149 km) from Lake
24
Figure 4. Coastal wetlands offshore from the mainland, include salt marsh (estuarine emergent) (A), shoals (B), tidal flats (C)
and bars. National Aerial Photography Program, color infrared photograph,coastal Louisiana, 2004.
Pontchartrain to the furthest extent
of estuarine wetland resources.
In this area, saltwater was the
overriding influence on biological
systems. The coastal zone in this
study was not synonymous with any
state or federal jurisdictional coastal
zone definitions. The legal definition
of “coastal zone” has been developed
for use in coastal demarcations,
planning, regulatory and
management activities undertaken
by other federal or state agencies.
To permit even spatial coverage
of the sample plots and to allow
results to be computed easily by
sets of states, the 36 physiographic
regions formed by the Hammond
subdivisions and the coastal zone
stratum were intersected with state
boundaries to form 220 subdivisions
or strata. An example of this
stratification approach and the way
it relates to sampling frequency is
shown for North Carolina (Figure 5).
In the physiographic strata
described above, weighted, stratified
sample plots were randomly
allocated in proportion to the amount
of wetland acreage expected to occur
in each stratum. Each sample area
was a surface plot 2.0 miles (3.2
km) on a side or 4.0 square miles
of area equaling 2,560 acres (1,036
ha). The study included all wetlands
regardless of land ownership.
This study re-analyzed the land area
for 4,371 existing sample plots used
for past wetlands status and trends
studies. Three hundred eleven
supplemental sample plots were
added to Ohio, Indiana, Illinois,
Iowa, Missouri, North Dakota,
South Dakota, California, Oklahoma
and Texas. Augmentation was done
to provide more finite measurement
and equitable spatial coverage of
plots, since loss rates had been
declining historically. This brought
the total number of sample plots
used in this study to 4,682.
25
Figure 5. Physiographic subdivisions of North Carolina and sample plot distribution as used in this study.
Sample Plot Location
Dry
Wet
Gulf-Atlantic Rolling Plain
Appalachian
Highlands
Gulf-Atlantic Coastal Flats
Coastal
Zone
Types and Dates
of Imagery
Image analysts relied primarily
on observable physical or spectral
characteristics evident on high
altitude imagery, in conjunction with
collateral data, to make decisions
regarding wetland classification and
deepwater determinations .
3Analysis of imagery was supplemented
with substantial field work and ground
observations.
Figure 6. High resolution, infrared Ikonos satellite image of bogs (A), lakes (B) and wetlands (C) of northern Wisconsin, spring
2005. Image courtesy of Space Imaging Corp.
Remote sensing techniques to detect
and monitor wetlands in the United
States and Canada have been used
successfully by a number academic
researchers and governmental
agencies (Dechka et al. 2002;
Watmough et al. 2002; Tiner 1996;
National Research Council 1995;
Patience and Klemas 1993; Lillesand
and Kiefer 1987; Aldrich 1979). The
use of remotely sensed data, either
from aircraft or satellite, is a cost
effective way to conduct surveys
over expansive areas (Dahl 1990a).
The Fish and Wildlife Service has
used remote sensing techniques to
determine the biological extent of
wetlands for the past 30 years. To
monitor wetland change, only high
quality imagery was acquired and
used.
26
This study used multiple sources
of recent imagery and direct on-the-
ground observations to record
wetland changes. To recognize and
classify wetland vegetation, color
infrared imagery was preferred
(Figure 6). Experienced wetland
interpreters have found color
infrared to be superior to other
imagery types for recognition and
classification of wetland vegetation
types (USFWS 2004b).
Figure 7. Early spring 2005 Ikonos satellite image of Michigan. Leaf-off condition made recognition of wetland features easier.
These old oxbows or swales (indicated by red arrows) can be masked by heavy tree canopy later in the growing season. Image
courtesy of Space Imaging Corp.
Wherever possible, leaf-off (early
spring or late fall) imagery was
used. Imagery obtained when
vegetation was dormant allowed
for better identification of wetland
boundaries, areas covered by water,
drainage patterns, separation of
coniferous from deciduous forest,
and classification of some understory
vegetation (Tiner 1996). There are
distinct advantages to using leaf-off
imagery to detect the extent of
forested wetlands. Leaf off imagery
enhances the visual evidence of
hydrologic conditions such as
saturation, flooding, or ponding
(Figure 7). This imagery, combined
with collateral data including soil
surveys, topographic maps, and
wetland maps were used to identify
and delineate the areal extent of
wetlands.
27
Figure 8. Mean date of imagery used by state.
In 2004, recent aerial photographic
coverage for large portions of the
country was not available. Multiple
sources of satellite imagery in
combination with recently acquired
digital photography were used
to complete this study. Satellite
imagery made up about 45 percent
of the source material used for
this analysis. Advantages included
higher resolution digital imagery
that was acquired close to the target
reporting date. The mean dates
of the imagery used, by state, are
shown in Figure 8.
Satellite imagery was supplemented
with National Agriculture Imagery
Program (NAIP) imagery acquired
during the agricultural growing
season (Figure 9). NAIP imagery
made up about 30 percent of the
source imagery. (For technical
specifications of NAIP imagery
see www.apfo.usda.gov/NAIP/ .)
The remaining imagery needed to
complete the study was acquired
through various sources of high
resolution aerial photography.
28
2003
2004
2005
California
Oregon
Idaho
Montana
Wyoming
Nevada
Utah
Colorado
North Dakota
South Dakota
Nebraska
Kansas Missouri
Illinois
Wisconsin
Michigan
Indiana
Ohio
Kentucky
Virginia
Florida
South
Carolina
Georgia
North
Carolina
Pennsylvania
New Jersey
New Hampshire
Maryland
Delaware
Connecticut
Massachusetts
Vermont Maine
New York
Rhode Island
West
Virginia
Tennessee
Mississippi
Alabama
Arkansas
Louisiana
Texas
Iowa
Minnesota
Oklahoma
New Mexico
Arizona
Washington
Figure 9. True color NAIP photographs show
farmland (A), forest (B) and wetlands (C) above, and
newly-created ponds in a housing development (D) at
right. Indiana, 2003.
29
Figure 10. A small wetland basin estimated to have been about seven square meters. Some
wetlands this size were detectable using high resolution imagery.
Technological
Advances
Technological advances in the
quality of remotely sensed
imagery, computerized mapping
techniques, and modernization of
data management systems enhanced
the ability to capture more detailed
and timely information about the
nation’s wetlands. The use of these
technologies greatly improved the
administration, access, management
and integration of the spatial
data. Such advances required
modernization of procedural
techniques for image interpretation,
data capture and operational
management. Some of the data
modernization process involved
development of customized software
tools to execute tasks specific to
wetland attribution, provide logic
checking functions and verification
of the digital status and trends data.
These procedural updates were
incorporated into a revised technical
procedures and protocols manual
(USFWS 2004b).
Methods of Data
Collection and
Image Analysis
The delineation of wetlands through
image analysis forms the foundation
for deriving all subsequent products
and results. Consequently, a
great deal of emphasis has been
placed on the quality of the image
interpretation. The Fish and
Wildlife Service makes no attempt
to adapt or apply the products of
these techniques to regulatory or
legal authorities regarding wetland
boundary determinations or to
jurisdiction or land ownership, but
rather the information was used to
assist in making trend estimates
characterizing wetland habitats.
General information on photo
interpretation techniques is
provided by various authors (Avery
1968; Lillesand and Kiefer 1987;
Philipson 1996). Specific protocols
used for image interpretation of
wetlands are documented in the
Status and Trends technical manual
(USFWS 2004b).
Wetlands were identified based on
vegetation, visible hydrology and
geography. Delineations on the
sample plots reflected ecological
change or changes in land use that
influenced the size, distribution or
classification of wetland habitats.
The minimum targeted delineation
unit for wetland was one acre
(0.40 ha). The actual smallest size
of wetland features delineated
was about 0.005 acres (0.002 ha).
However, not all features this size,
or smaller, were detected (Figure
10).
30
Wetland Change
Detection
Remotely sensed imagery was the
primary data for wetland change
detection. It was used in conjunction
with reliable collateral data such
as topographic maps, coastal
navigation charts, soils information,
and historical imagery or studies.
Field verification also played an
important role and was used to
address questions regarding image
interpretation, land use classification
and attribution of wetland gains or
losses.
For each sample plot, the extent
of change among all wetland types
between the two dates of imagery
was used to estimate the total area
of each wetland type (Figure 11)
and the changes in wetland area and
type between the two dates. The
changes were recorded in categories
that can be considered the result
of either natural change, such as
the natural succession of emergent
wetlands to shrub wetlands, or
human induced change. Areas of
sample plots that were identified
in the initial era as wetland but are
no longer wetland were placed into
five land use categories (agriculture,
upland forested plantations,
upland areas of rural development,
upland urban landscapes and other
miscellaneous lands) based upon
the land use evident on the most
recent imagery. The outputs from
this analysis were change matrices
that provided estimates of wetland
area by type and observed changes
Figure 11. Change detection involved a comparison of plots at two different times (T1 and T2).
over time. Rigorous quality control
inspections were built into the
interpretation, data collection and
analysis processes.
Difficulties in determining wetland
change can be related to timing
or quality of the imagery (Dahl
2004). Imagery acquired at the
time of abnormal hydrologic
conditions, such as flooding or
drought, can make determination
of wetland change challenging.
In these instances field work was
required to assist image analysts
in making appropriate wetlands
determinations.
Misinterpretation of wetland loss or
gain could result from factors such
as farming of wetlands during dry
cycles, drought conditions, excess
T1 T2
6 years
31
surface water or flooding. False
changes were avoided by observing
visual evidence of a change in
land management practices. This
included the presence of new
drainage ditches (Figure 12),
canals or other man-made water
courses, evidence of dredging, spoil
deposition or fills, impoundments or
excavations, structures, pavement or
hardened surfaces, in addition to the
lack of any hydrology, vegetation or
soil indicators indicative of wetland.
Some land use practices can also
affect wetland change detection.
Disturbed sites often had ambiguous
remotes sensing indicators.
Disturbed areas were indicative
of lands in transition from one
Figure 13. Lands in transition from
one land use category to another pose
unique challenges for image analysts.
Field inspection of this site indicated
the area was under construction as part
of a highway project.
land use to another (Figure 13).
Upon field inspection, these areas
often had altered hydrology,
soils or vegetation making
wetland classification and change
determination more difficult. In
these instances, field inspection of
the wetland site and surrounding
area provided additional
information.
Figure 12. A true color aerial
photograph shows a new drainage
network (indicated by red arrow)
and provides visual evidence of
wetland loss. Lack of wetland
vegetation, surface water or soil
saturation further indicates that
this wetland had been effectively
drained.
32
Field
Verification
Field verification was completed
for 1,504 (32 percent) of the sample
plots distributed in 35 States
(Figure 14). This constituted
the largest field verification
effort undertaken for a status
and trends report. Field work
was done primarily as a quality
control measure to verify that
plot delineations were correct.
Verification involved field visits to a
cross section of wetland types and
geographic settings, and to plots
with different image types, scales
and dates. Field work was not done
in some western states because of
the remote location (limited access)
of sample plots. Of the 1,504 sample
plots reviewed in the field, 720 used
satellite imagery and 784 used high
altitude aerial photography. All
field verification work took place
between March and September,
2005 . Representatives from four
states and seven federal agencies
participated in field reconnaissance
trips. In rare instances, field work
was used to update sample plots
based on observations of on-the-ground
conditions.
4 Results of field verification work indicated
no discernable differences in the size or
classification of wetlands delineated using
either satellite imagery or the high altitude
photography. Errors of wetland omission
were two percent based on occurrence
but less than one percent based on area
(omitted wetlands were generally small <
1.0 acre or 2.47 ha). Errors of inclusion of
upland were less than one percent in both
occurrence and area. There was no difference
regionally, between states or data analysts
in the number of errors found based on
field inspections, although not all plots were
included in the field analysis.
Figure 14. Field verification was completed at sites in 35 states shown on the map.
33
States not field verified
States field verified
California
Oregon
Idaho
Montana
Wyoming
Nevada
Utah
Colorado
North Dakota
South Dakota
Nebraska
Kansas Missouri
Illinois
Wisconsin
Michigan
Indiana
Ohio
Kentucky
Virginia
Florida
South
Carolina
Georgia
North
Carolina
Pennsylvania
New Jersey
New Hampshire
Maryland
Delaware
Connecticut
Massachusetts
Vermont Maine
New York
Rhode Island
West
Virginia
Tennessee
Mississippi
Alabama
Arkansas
Louisiana
Texas
Iowa
Minnesota
Oklahoma
New Mexico
Arizona
Washington
Quality Control
To ensure the reliability of wetland
status and trends data, the Fish
and Wildlife Service adhered to
established quality assurance and
quality control measures for data
collection, analysis, verification and
reporting. Some of the major quality
control steps included:
Plot Location and Positional
Accuracy
Status and trends sample plots were
permanently fixed georeferenced
areas used to monitor land use and
cover type changes. The same plot
population has been re-analyzed
for each status and trends report
cycle. The plot coordinates were
positioned precisely using a system
of redundant backup locators on
prints produced from a geographic
information system, topographic
maps (Figure 15), other maps
used for collateral information and
the aerial imagery. Plot outlines
were computer generated for the
correct spatial coordinates, size and
projection (Figure 16).
Quality Control of Interpreted Images
This study used well established,
time-tested, fully documented data
collection conventions (USFWS
1994a; 1994b; 2004b). It employed
a small cadre of highly skilled and
experienced personnel for image
interpretation and processing.
All interpreted imagery was
reviewed by a technical expert in
ecological change detection. The
reviewing analyst adhered to all
standards, quality requirements and
technical specifications and reviewed
100 percent of the work.
Data Verification
All digital data files were subjected
to rigorous quality control
inspections. Digital data verification
included quality control checks
that addressed the geospatial
correctness, digital integrity and
some cartographic aspects of
the data. These steps took place
following the review and qualitative
acceptance of the ecological data.
Implementation of quality checks
ensured that the data conformed to
the specified criteria, thus achieving
the project objectives.
Quality Assurance of Digital Data
Files
There were tremendous advantages
in using newer technologies to store
and analyze the geographic data.
The geospatial analysis capability
built into this study provided a
complete digital database to better
assist analysis of wetland change
information.
All digital data files were subjected
to rigorous quality control
inspections. Automated checking
modules incorporated in the
geographic information system
(Arc/GIS) were used to correct
digital artifacts including polygon
topology. Additional customized
data inspections were made to
ensure that the changes indicated
at the image interpretation stage
were properly executed. Digital file
quality control reviews also provided
confirmation of plot location,
stratum assignment, and total land
or water area sampled.
A customized digital data
verification software package
designed specifically for status
and trends work was used. It
checked for improbable changes
that may represent errors in the
image interpretation. The software
considered the length of time
between update cycles, identified
certain unrealistic cover-type
changes such open water ponds
changing to forested wetland, and
other types of potential errors in the
digital data.
34
Figure 15. Topographic maps in digital
raster graphics format were used as
auxilliary information and for quality
control.
Figure 16. Digital wetlands status and trends data were viewed combined with contemporary georeferenced color infrared
imagery of the study areas.
35
Statistical
Analysis
The wetland status and trends
study was based on a scientific
probability sample of the surface
area of the 48 conterminous States.
The area sampled was about 1.93
billion acres (0.8 billion ha), and
the sampling did not discriminate
based on land ownership. The study
used a stratified, simple random
sampling design. About 754,000
possible sample plots comprised
the total population. Given this
population, the sampling design was
stratified by use of the 36 physical
subdivisions described in the “Study
Design” section. This stratification
scheme had ecological, statistical,
and practical advantages. The
study design was well suited for
determining wetland acreage trends
because the 36 divisions of the
United States coincide with factors
that effect wetland distribution
and abundance. Once stratified,
the land subdivisions represented
large areas where the samples were
distributed to obtain an even spatial
representation of plots. The final
stratification, based on intersecting
physiographic land types with state
boundaries, guaranteed an improved
spatial random sample of plots.
Geographic information system
software organized the information
about the 4,682 random sample
plots. An important design feature
crucial to understanding the
technical aspects of this study is
that a grid of full-sized square plots
can be overlaid on any stratum to
define the population of sampling
units for that stratum. However, at
the stratum boundaries some plots
were “split” across the boundary
and thus, were not a full 2,560 acres
(1,036 ha). In sampling theory, plot
size is an auxiliary variable that is
known for all sampled plots and
whose total is known over every
stratum. All sampling units (plots) in
a stratum were given equal selection
probabilities regardless of their
size. In the data analysis phase, the
adjustments were made for varying
plot sizes by use of ratio estimation
theory. For any wetland type, the
proportion of its area in the sample
of plots in a stratum was an unbiased
estimator of the unknown proportion
of that type in that stratum.
Inference about total wetland
acreage by wetland type or for all
wetlands in any stratum began with
the ratio (r) of the relevant total
acreage observed in the sample (Ty),
for that stratum divided by the total
area of the sample (Tx). Thus, y
was measured in each sample plot;
r = Ty/Tx, and the estimated total
acreage of the relevant wetland type
in the stratum was A x r. The sum
of these estimated totals over all
strata provided the national estimate
for the wetland type in question.
Uncertainty, which was measured
as sampling variance of an estimate,
was estimated based on the variation
among the sample proportions in a
stratum (the estimation of sample
variation is highly technical and
not presented here). The sampling
variation of the national total was
the sum of the sampling variance
over all strata. These methods are
standard for ratio estimation in
association with a stratified random
sampling design (Sarndal et al. 1992;
Thompson 1992).
By use of this statistical procedure,
the sample plot data were expanded
to specific physiographic regions,
by wetland type, and statistical
estimates were generated for the 48
conterminous States. The reliability
of each estimate generated is
expressed as the percent coefficient
of variation (% C.V.) associated with
that estimate. Percent coefficient of
variation was expressed as (standard
deviation/mean) x (100). The percent
coefficient of variation indicates that
there was a 95 percent probability
that an estimate was within the
indicated percentage range of the
true value.
Procedural Error
Procedural or measurement errors
occur in the data collection phase of
any study and must be considered.
Procedural error is related to the
ability to accurately recognize
and classify wetlands both from
multiple sources of imagery and
on-the-ground evaluations. Types of
procedural errors may have included
missed wetlands, inclusion of
upland as wetland, misclassification
of wetlands or misinterpretation
of data collection protocols. The
amount of introduced procedural
error is usually a function of the
quality of the data collection
conventions; the number, variability,
training and experience of data
collection personnel; and the rigor
of any quality control or quality
assurance measures.
Rigorous quality control reviews
and redundant inspections were
incorporated into the data collection
and data entry processes to help
reduce the level of procedural error.
Estimated procedural error ranged
from 3 to 5 percent of the true values
when all quality assurance measures
had been completed.
36
Limitations
The identification of wetland
habitats through image analysis
forms the basis for wetland status
and trends data results. Because of
the limitations of aerial imagery as
the primary data source to detect
some wetlands, the Fish and Wildlife
Service excludes certain wetland
types from its monitoring efforts.
These limitations included the
inability to detect small areas;
inability to accurately map or
monitor certain types of wetlands
such as sea grasses (Orth et
al. 1990), submerged aquatic
vegetation, or submerged reefs
(Dahl 2005); and inability to
consistently identify certain forested
wetlands (Tiner 1990).
Other habitats intentionally
excluded from this study include:
Estuarine wetlands of the Pacific
coast—Unlike the broad expanses
of emergent wetlands along the
Gulf and Atlantic coasts, the
estuarine wetlands of California,
Oregon and Washington occur in
discontinuous patches (Figure
17). Their patchy distribution
precludes establishment of a coastal
stratum similar to that of the Gulf
and Atlantic coast wetlands and
no statistically valid data could be
obtained through establishment of a
Pacific coastal stratum. Therefore,
consistent with past studies, this
study did not sample Pacific coast
estuarine wetlands such as those
in San Francisco Bay, California;
Coos Bay, Oregon; or Puget Sound,
Washington.
Figure 17. The Pacific coastline, Three Arch Rocks National Wildlife Refuge, Oregon. Photo courtesy of FWS.
37
Figures 18A and B. Commercial rice
fields where water was pumped to flood
the rice crop. These fields were drained
when they were in upland crop rotation.
Central Arkansas, 2005.
Commercial Rice—Throughout
the southeastern United States and
in California, rice (Oryza sativa)
is planted on drained hydric soils
and on upland soils. When rice was
being grown, the land was flooded
and the area functioned as wetland
(Figures 18A and B). In years when
rice was not grown, the same fields
were used to grow other crops (e.g.,
corn, soybeans, cotton). Commercial
rice lands were identified primarily
in California, Arkansas, Louisiana,
Mississippi and Texas. These
cultivated rice fields were not able
to support hydrophytic vegetation.
Consequently, the Fish and Wildlife
Service did not include these lands in
the base wetland acreage estimates.
38
A
B
Agricultural activity was shown by
distinctive geometric field and road
patterns on the landscape and/or
by tracks produced by livestock or
mechanized equipment. Agricultural
land uses included horticultural
crops, row and close grown crops,
hayland, pastureland, native
pastures and range land and farm
infrastructures (Figure 19A and B).
Examples of agricultural activities in
each land use include:
Horticultural crops consisted of
orchard fruits (limes, grapefruit,
oranges, other citrus, apples,
peaches and like species). Also
included were nuts such as almonds,
pecans and walnuts; vineyards
including grapes and hops; bush-fruit
such as blueberries; berries such
as strawberries or raspberries; and
commercial flower and fern growing
operations.
Attribution of
Wetland Losses
The process of identifying or
attributing cause for wetland losses
or gains has been investigated by
both the Fish and Wildlife Service
and Natural Resources Conservation
Service. In 1998 and 1999, the
Natural Resources Conservation
Service and the Fish and Wildlife
Service made a concerted effort
to develop a uniform approach to
attribute wetland losses and gains
to their causes. The categories used
to determine the causes of wetland
losses and gains are described below.
Agriculture
The definition of agriculture
followed Anderson et al. (1976)
and included land used primarily
for production of food and fiber.
Row and Close Grown Crops
included field corn, sugar cane,
sweet corn, sorghum, soybeans,
cotton, peanuts, tobacco, sugar
beets, potatoes, and truck crops
such as melons, beets, cauliflower,
pumpkins, tomatoes, sunflower and
watermelon. Close grown crops also
included wheat, oats, barley, sod,
ryegrass, and similar graminoids.
Hayland and pastureland included
grass, legumes, summer fallow and
grazed native grassland.
Other farmland included
farmsteads and ranch headquarters,
commercial feedlots, greenhouses,
hog facilities, nurseries and poultry
facilities.
Figure 19A and B. Examples of agricultural land use include both
this rangeland in western Nebraska, 2005 (A), and row crops such
as this cornfield in the midwest, 2004 (B).
39
A
B
Forested Plantations
Forested plantations consisted
of planted and managed forest
stands and included planted pines,
Christmas tree farms, clear cuts and
other managed forest stands. These
were identified by the following
remote sensing indicators: 1) trees
planted in rows or blocks; 2) forested
blocks growing with uniform crown
heights; or 3) logging activity and
use patterns (Figure 20).
Figure 20. Trees planted in rows with uniform crown height (A) and block clear cuts [blue-green feature in center (B) were
indicators of managed forest plantations. Color infrared Ikonos satellite image, Virginia 2004. Courtesy of Space Imaging Corp.
Rural Development
Rural developments occurred in
rural and suburban settings outside
distinct cities and towns. They were
characterized by non intensive land
use and sparse building density.
Typically, a rural development was
a crossroads community that had a
corner gas station and a convenience
store and was surrounded by
sparse residential housing.
Scattered suburban communities
located outside of a major urban
centers were also included in this
category as were some industrial
and commercial complexes;
isolated transportation, power,
and communication facilities; strip
mines; quarries; and recreational
areas such as golf courses.
Major highways through rural
development areas were included in
the rural development category.
40
Urban Development
Urban land consisted of areas of
intensive use in which much of the
land was covered by structures
(high building density as shown in
Figure 21). Urbanized areas were
cities and towns that provided
goods and services through a
central business district. Services
such as banking, medical and legal
office buildings, supermarkets and
department stores made up the
business center of a city. Commercial
strip developments along main
transportation routes, shopping
centers, contiguous dense residential
areas, industrial and commercial
complexes, transportation, power
and communication facilities, city
parks, ball fields and golf courses
were included in the urban category.
Other Land Uses
Other Land Use was composed
of uplands not characterized by
the previous categories. Typically
these lands included native prairie,
unmanaged or non patterned upland
forests, conservation lands, scrub
lands, and barren land. Lands in
transition between different uses
were also in this category.
Transitional lands were lands in
transition from one land use to
another. They generally occurred
in large acreage blocks of 40
acres (16 ha) or more. They were
characterized by the lack of any
remote sensor information that
would enable the interpreter to
reliably predict future use. The
transitional phase occurred when
wetlands were drained, ditched,
filled or when the vegetation had
been removed and the area was
temporarily bare.
Interagency field evaluations were
conducted to test these definitions
on the wetland status and trends
plots to attribute wetland losses or
gains. Field evaluation of these plots
resulted in no disagreement among
agency representatives with how the
Fish and Wildlife Service attributed
wetland losses or gains as to cause.
Figure 21. Urban wetlands (shown as dark blue-black) outside of a shopping mall are surrounded by high density urban
development. New Jersey, 2003, color infrared photograph.
41
A freshwater wetland, Reelfoot Lake, Tennessee, 2005.
42
Results and Discussion
Status of the Nation’s Wetlands
There were an estimated 107.7
million acres (43.6 million ha) of
wetlands in the conterminous
United States in 2004 . (The
coefficient of variation of the
national estimate was 2.7
percent. ) Wetlands composed
5.5 percent of the surface area
of the conterminous United
States (Figure 22). An estimated
95 percent of all wetlands were
freshwater and five percent were
in estuarine or marine systems.
This overall distribution of
wetlands by area and type had not
changed from the previous era.
5 This estimate reflects a 2.0 percent
adjustment to the national wetland acreage
base. This adjustment is within the 3
percent coefficient of variation associated
with this estimation.
6 95 percent confidence interval
Figure 22. Wetland area compared to the total land area of the
conterminous United States, 2004.
Data for the 1998 to 2004 study
period are presented in a change
matrix and shown in Appendix C.
For ease of use, those data have
been summarized and presented in
Table 2.
Within the estuarine system,
estuarine emergent (salt marsh—
Figure 23) dominated, making up
an estimated 73 percent (almost 3.9
million acres or 1.6 million ha) of
all estuarine and marine wetlands.
Estuarine shrub wetlands made
up 13 percent of the area and non-vegetated
saltwater wetlands 14
percent (Figure 24).
Among freshwater wetlands (Figure
25), freshwater forested wetlands
made up the single largest category
(51 percent). Freshwater emergent
wetland made up an estimated 25.5
percent of the total area, shrub
wetlands 17 percent and freshwater
ponds 6.5 percent.
43
Upland
93.5%
Total Land Area
Deepwater*
1%
Wetland
5.5%
*Excludes area of the
Great Lakes
Table 2. Change in wetland area for selected wetland and deepwater categories, 1998 to 2004. The coefficient of
variation (CV) for each entry (expressed as a percentage) is given in parentheses.
Area, In Thousands of Acres
Wetland/Deepwater Category Estimated Area,
1998
Estimated Area,
2004
Change,
1998–2004
Change
(In Percent)
Marine 130.4
(20.2)
128.6
(20.5)
–-1/9
(68.7) –1.4
Estuarine Intertidal Non-Vegetated1 594.1
(10.7)
600.0
(10.3)
5.9
* 1.0
Estuarine Intertidal Vegetated2 4,604.2
(4.0)
4,571.7
(4.0)
–32.4
(32.7) –0.7
All Intertidal Wetlands 5,328.7
(3.8)
5,300.3
(3.8)
–28.4
(48.6) –0.5
Freshwater Non-Vegetated3 5,918.7
(3.7)
6,633.9
(3.5)
715.3
(12.8) 12.1
Freshwater Ponds4 5,534,3
(3.7)
6,229.6
(3.5)
695.4
(13.1) 12.6
Freshwater Vegetated5 96,414.9
(3.0)
95,819.8
(3.0)
–495.1
(35.0) –0.5
Freshwater Emergent 26,289.6
(8.0)
26,147.0
(8.0)
–142.6
* –0.5
Freshwater Forested 51,483.1
(2.8)
52,031.4
(2.8)
548.2
(56.1) 1.1
Freshwater Shrub 18,542.2
(4.1)
17,641.4
(4.3)
–900.8
(34.2) –4.9
All Freshwater Wetlands 102,233.6
(2.9)
102,453.8
(2.8)
220.2
(77.3) 0.2
All Wetlands 107,562.3
(2.7)
107,754.0
(2.7)
191.8
(89.1) 0.2
Deepwater Habitats
Lacustrine5 16,610.5
(10.4)
16,773.4
(10.2)
162.9
(76.2) 1.0
Riverine 6,765.5
(9.1)
6,813.3
(9.1)
47.7
(68.8) 0.7
Estuarine Subtitdal 17.680.5
(2.2)
17.717.8
(2.2)
37.3
(40.8) 0.2
All Deepwater Habitats 41,046.6
(4.6)
41,304.5
(4.5)
247.9
(51.7) 0.6
All Wetlands and Deepwater Habitats1,2 148,618.8
(2.4)
149,058.5
(2.4)
439.7
(31.3) 0.3
*Statistically unreliable.
1 Includes the categories: Estuarine Intertidal Aquatic Bed and Estuarine Intertidal Unconsolidated Shore.
2 Includes the categories: Estuarine Intertidal Emergent and Estuarine Intertidal Shrub.
3 Includes the categories: Palustrine Aquatic Bed, Palustrine Unconsolidated Bottom and Palustrine Unconsolidated Shore.
4 Includes the categories: Palustrine Aquatic Bed, Palustrine Unconsolidated Bottom.
5 Includes the categories: Palustrine Emergent, Palustrine Forested and Palustrine Shrub.
6 Does non include the open-water area of the Great Lakes.
Percent coefficient of variation was expressed as (standard deviation/mean) x 100.
44
Figure 24. Percentage of
estimated estuarine and
freshwater wetland area and
covertypes, 2004.
Figure 23. Salt marsh along the Ecofina
River, Florida.
Figure 25. A freshwater wetland in the
southeastern United States, 2005.
Estuarine Wetlands
Total Wetlands
Freshwater
95%
Estuarine
5%
Emergents
73%*
Flats/Beaches
14%
Shrubs
13%
Freshwater Wetlands
Forested
51%
Emergents
25.5%*
Shrubs
17%
Ponds
6.5%
*Denotes change from
previous era
45
National Trends, 1998 to 2004
Between 1998 and 2004 there was
an estimated net gain (Table 3) in
wetlands of 191,750 acres (77,630
ha). This equated to an average
annual net gain of about 32,000
acres (12,900 ha) as seen in Figure
26. These estimates have led to the
conclusion that wetland area gains
achieved through restoration and
creation have outdistanced losses.
These data indicate a net gain in
acreage but this report does not
draw conclusions regarding trends
in quality of the nation’s wetlands
7 There are statistical uncertainties associated
with this estimate. The coefficient of variation
expressed as a percentage is 89.1 percent for
the net gain estimate.
Intertidal wetlands declined by
an estimated 28,416 ac (11,500 ha)
from 1998 to 2004. This was an
average annual loss of about 4,740
acres (1,920 ha). The majority of
these losses (94 percent) were to
deepwater bay bottoms or open
ocean.
Almost all net gains of wetland
observed between 1998 and 2004
were in freshwater wetland types.
The estimated net gain in freshwater
wetland area between 1998 and 2004
was 220,200 acres (89,140 ha) as
Figure 26. Average annual net loss and gain estimates for the conterminous United States, 1954 to 2004. Sources: Frayer et al.
1983; Dahl and Johnson 1991; Dahl 2000; and this study.
seen in Table 2. Forested wetlands
experienced a net gain. This can
be explained by the maturation of
wetland shrubs to forested wetlands.
There was also a substantial increase
in the number of open water ponds.
Pond area increased by an estimated
12.6 percent over this study period.
46
100,000
0
-100,000
-200,000
-300,000
-400,000
-500,000
Gains
+32,000
Losses
-58,550
-290,000
-458,000
1950s–1970s 1970s–1980s 1980s–1990s
Acres
1998–2004
Attribution of
Wetland Gain
and Loss
Figure 27 depicts the categories
that contributed wetland gains and
those responsible for wetland losses
over the course of this study. A net
gain in wetland area was attributed
to conversion of agricultural lands
or former agricultural lands that
had been idled in combination
with wetland restorations from
conservation lands in the “other”
land use category.
Some freshwater wetland
losses attributed to urban, rural
development and silviculture offset
some of the gains. An estimated
88,960 acres (36,000 ha) or 39
percent of the wetland losses, were
lost to urban developments, 51,440
acres (20,800 ha), 22 percent were
lost to rural development and
18,000 acres (7,300 ha), 8 percent
of wetlands were lost through
drainage or filling for silviculture.
These losses were all the result of
actions that destroyed the wetland
hydrology. An additional 70,100
acres (28,400 ha), or 31 percent
of the wetland area lost between
1998 and 2004 became deepwater
habitats.
There were net gains from the
“other” lands category and from
Agriculture as a result of wetland
restoration and conservation
programs. An estimated 70,700
wetland acres (28,600 ha) came from
agricultural lands and 349,600 acres
(141,500 ha) from “other” uplands.
These gains represented 17 percent
of the net wetland gains from
Agriculture and 83 percent from
“other” uplands. Since the “other”
uplands category includes lands in
transition some of these wetlands
may be subject to loss over time.
Representative wetland restoration
programs are listed in Appendix D.
Using the study definitions for
the causes of wetland losses and
gains, it was determined that urban
development and rural development
accounted for an estimated 140,400
acres (56,840 ha) or 61 percent of
wetland loss over the course of this
study.
Figure 27. Wetlands gained or lost from upland categories and deepwater, 1998 to 2004.
47
Deepwater
-70,100
Urban
-88,960
Rural
Development
-51,440
Land Use Category
Silviculture
-18,000
Agriculture
+70,770
Other
+349,600
0
20
-20
-40
-60
-80
-90
40
60
80
400,000
Acres (in Thousands)
Gains
Losses
Intertidal
Estuarine and
Marine Wetland
Resources
Three major categories of estuarine
and marine wetlands were included
in this study: estuarine intertidal
emergents (salt and brackish water
marshes), estuarine shrub wetlands
(mangrove swamps or mangles and
other salt tolerant woody species)
and estuarine and marine intertidal
non-vegetated wetlands. This latter
category included exposed coastal
beaches subject to tidal flooding,
shallow water sand bars, tidal flats,
tidally exposed shoals and sand
spits.
The vegetated components of the
estuarine and marine systems
are among the most biologically
productive aquatic ecosystems in
the world (Kennish 2004). Wetlands
along the nation’s coastline have
provided valuable resources and
supported large sections of the
nation’s economy (USEPA 2004).
Wetlands have also provided
opportunities for recreation and
supported commercially valuable
fish and crustacean populations.
Estuarine and wetland dependent
Figure 28. Composition of marine and estuarine intertidal wetlands, 2004.
fish and shellfish species accounted
for about 75 percent of the total
annual seafood harvest in the United
States (Weber 1995). In the Gulf of
Mexico, coastal waters attracted
millions of sport fishermen and
beach users as tourism in the Gulf
coast states contributed over $20
billion to the nation’s economy
(USEPA 1999). The importance
of both estuarine and freshwater
wetlands to fish populations, and
sport and commercial fishing
cannot be overemphasized. This
link between wetlands and aquatic
species includes ecological processes
that are important for maintaining
food webs, land and water
interactions, and environmental
quality. Wetland loss and its effect
on fish populations are among the
many issues forcing a re-evaluation
of activities on the landscape (NOAA
2001).
Estuarine and marine wetlands
have been particularly susceptible
to the various stressors resulting
from rapid population growth and
development within the coastal
watersheds nationwide (Kennish
8 The importance of wetlands to fish
populations is discussed in the insert section
“Wetlands and Fish.”
2004). From the 1950s to 1970s,
estuarine wetlands were dredged
and filled extensively for residential
and commercial development and
for navigation (Hefner 1986). To
help conserve the nation’s valuable
coastal resources, numerous
measures have been taken to protect
estuarine and marine resources.
Since the mid 1970s, many of the
nation’s shoreline habitats have
been protected either by regulation
or public ownership. These
mechanisms, in combination with
outreach and educational efforts,
have been responsible for reducing
intertidal wetlands losses in Florida
(Dahl 2005).
This study estimated that in 2004
there were slightly more than 5.3
million acres (2.1 million ha) of
marine and estuarine wetlands in
the conterminous United States.
Eighty six percent of that total area
was vegetated wetland (Figure 28).
Collectively, intertidal wetlands
declined by an estimated 28,416
ac (11,580 ha) between 1998 and
2004. Estuarine vegetated wetlands
declined by an estimated 32,400
acres (13,120 ha) between 1998
and 2004. Estuarine non-vegetated
wetlands experienced a net gain of
an estimated 4,000 ac (1,620 ha);
marine intertidal shorelines declined
by 1,900 ac (770 ha).
48
All Intertidal Wetlands
Estuarine Vegetated Wetlands
Vegetated
86%
Non-vegetated
14%
Emergents
85%
Shrubs
15%
Table 3. Changes to estuarine and marine wetlands, 1998 to 2004. The coefficient of variation (CV) for each entry
(expressed as a percentage) is given in parentheses.
Area, In Thousands of Acres
Wetland Category Estimated Area,
1998
Estimated Area,
2004
Gain or Loss,
1998–2004
Change
(In Percent)
Area (as Percent)
of All Intertidal
Wetland, 2004
Marine Intertidal 130.4
(20.2)
128.6
(20.5)
–1.9
(68.7) –1.4 2.4
Estuarine Unconsolidated Shore 563.2
(10.8)
567.5
(10.4)
4.3
* 10.7
Estuarine Aquatic Bed 30.8
(27.1)
32.4
(26.0)
1.6
(63.6) 0.6
Marine and Estuarine Intertidal
Non-Vegetated
724.5
(9.8)
728.5
(9.5)
4.0
* 0.5 13.7
Estuarine Emergent 3,922.8
(4.2)
3,889.5
(4.2)
–33.2
(31.8) 73.4
Estuarine Shrub 681.4
(12.5)
682.2
(12.5)
0.8
* 12.9
Estuarine Intertidal Vegetated1 4,604.2
(4.0)
4,571.7
(4.0)
–32.4
(32.6) –0.7 86.3
Changes in Coastal Deepwater area, 1998–2004
Estuarine Subtitdal 17,680.5
(2.2)
17,717.8
(2.2)
37.3
(40.8) — —
*Statistically unreliable.
1 Includes the categories: Estuarine Emergent and Estuarine Shrub.
Excludes marine and estuarine wetlands of California, Oregon and Washington.
Percent coefficient of variation was expressed as (standard deviation/mean) x (100).
open saltwater systems (Figure 29).
This was due to natural and man-induced
activities such as dredging,
water control, and commercial and
recreational boat traffic . The losses
of estuarine emergents exceeded the
total net loss of all other intertidal
estuarine and marine wetlands
combined.
9 Losses reported here were prior to the
hurricanes of 2005. The Fish and Wildlife
Service is preparing to conduct follow-up
studies to reassess wetland changes along the
Gulf Coast.
The changes that occurred between
1998 and 2004 in estuarine and
marine wetlands are shown in Table
3. The largest acreage change was
an estimated net loss of 33,230 acres
(13,450 ha) of estuarine emergent
wetland. The greatest percent
change was a decline of 1.4 percent
of marine intertidal wetland.
The overriding factor in the decline
of estuarine and marine wetlands
was loss of emergent salt marsh to
Figure 29. Estimated percent
loss of intertidal estuarine and
marine wetlands to deepwater and
development, 1998 to 2004.
49
Deepwater
93%
Development
7%
Marine and
Estuarine
Beaches, Tidal
Bars, Flats and
Shoals
Sand, mud or rock beaches, bars
and shoals along the interface
with tidal saltwater composed the
non-vegetated intertidal wetlands
(Figure 30). These areas were
subject to dramatic changes
resulting from coastal storms,
hurricanes, tidal surge, sea level
rise, sediment deposition or various
forms of artificial manipulation
during this study period.
Ecologically, these wetlands are
important to a variety of fish and
wildlife species. Open sandy beach
Figure 30 . Non-vegetated tidal flats grade into sparsely vegetated beach ridges. These areas are important
for a variety of birds, sea turtles and other marine life. Florida, 2000.
habitats are particularly important
to nesting, foraging and loafing
waterbirds (Kushlan et al. 2002)
(Figure 31 and 32). The green sea
turtle (Chelonia mydas) and the
loggerhead sea turtle (Caretta
caretta) also use sandy beaches
for nesting sites. Shallow water
coastal flats are important for
sport fish such as the sand sea
trout (Cynoscion arenarius),
bonefish (Albuta vulpes), and snook
(Centropomus undecimalis).
There were an estimated 728,540
acres (294,960 ha) of intertidal non-vegetated
wetlands in 2004. This
study found that from 1998 to 2004
(Table 4) marine intertidal beaches
declined by 1,900 acres (770 ha),
a 1.4 percent decline. This was
very similar to the rate of decline
observed from 1986 to 1997, when
marine beaches declined 1.7 percent.
Estuarine bars, flats and shoals
(Figure 33) increased in area over
the same timeframe. There was an
estimated increase of 4,300 acres
(1,740 ha). This increase was largely
at the expense of estuarine emergent
salt marsh which was sloughed into
deeper water bays and sounds. Land
subsidence, saltwater intrusion and
coastal erosion processes may have
contributed to these changes.
Intertidal non-vegetated wetland
changes to urban and other forms
of upland development were not
statistically significant.
50
Figure 31. Intertidal marine beaches provide important
habitat for shorebirds. These types of wetlands declined by
1.4 percent between 1998 and 2004. Coastal Louisiana, 2005.
Photo by J. Harner, USGS. Figure 32. The black-necked stilt
(Himantopus mexicanus) inhabits mud
flats, pools, back water beaches, brackish
ponds of saltwater marshes and other
wetland habitats. Photo courtesy of FWS.
Figure 33. New shoals and sand bars are continually forming in shallow water areas. This image shows a new feature
(brightest white areas) off from the coast of Virginia, 2004.
51
Estuarine
Emergent
Wetlands
Estuarine emergent wetlands
(synonymous with the term “salt
marsh”) were found close to the
shoreline and were associated with
estuaries, lagoons, embayments,
sounds and coastal barriers
(Figure 34). Salinities ranged from
hypersaline to oligohaline (Cowardin
et al. 1979). The coastal plain of
the southeastern Atlantic and Gulf
States supported expansive areas
of intertidal estuarine wetlands,
particularly emergent salt marsh.
These marshes support diverse
animal life and are extremely
productive and ecologically
important features on the coastal
landscape. The abundance and
distribution of individual species
of both animals and plants are
influenced by physical conditions
including salinity, water depth,
tidal fluctuation and temperature
variations (Chabreck 1988).
There were an estimated 3,889,500
acres (1,574,700 ha) of estuarine
emergent salt marsh wetland in
2004.
Estuarine emergent wetland
declined by 33,230 acres (13,450
ha) between 1998 and 2004. This
represented a loss of 0.9 percent
of this wetland type. The average
annual rate of estuarine emergent
loss was 5,540 acres (2,240 ha). This
rate of loss was consistent with the
rate of salt marsh loss recorded from
1986 to 1997 (Dahl 2000). Urban and
rural development activities, and
the conversion of wetlands to other
upland land uses, accounted for an
estimated loss of 1,732 acres (700 ha)
or about 3.0 percent of all losses of
estuarine emergent wetland. Most
of the losses of estuarine emergent
wetland were due to loss to deep
salt water and occurred in coastal
Louisiana (Figure 35).
Numerous restoration and
rehabilitation projects have been
undertaken in Louisiana as part
of the Coastal Wetlands Planning,
Protection and Restoration Act of
1990, to begin the process of slowing
the rate of wetland loss in that
region (Zinn and Copeland 2002).
Despite these efforts, the rate of
estuarine wetland loss has remained
constant since the mid 1980s.
Projects undertaken in Louisiana
may have restored functional value
of some wetlands. Other restoration
efforts might have been directed
toward freshwater wetlands
elsewhere within “coastal” proximity
but outside of the estuarine and
marine systems.
Figure 34. High altitude infrared photograph of salt marsh (darker mottles) offshore from coastal Georgia, 2004.
52
Estuarine Emergent Wetland Loss
0–25 Acres
26–75 Acres
76–150 Acres
151–300 Acres
Texas
Texas
Louisiana
Louisiana
Mississippi
Mississippi
Alabama
Florida
Georgia
South Carolina
North Carolina
Virginia
Maryland
Delaware
New Jersey
Connecticut
Massachusetts
Vermont
New Hampshire Maine
Rhode
Island
Pennsylvania
New York
Figure 35. Estuarine emergent losses as observed in this study
along the Atlantic and Gulf of Mexico. Inset shows close up of
Louisiana where most losses occurred between 1998 and 2004.
53
Estimates of wetland loss from
this study were contrasted with
other estimates of wetland loss
in Louisiana as seen in Table 4.
Geographic dissimilarities and
terminology differences including
“coastal” versus “estuarine,”
“wetland” versus “land loss,” and
temporal differences accounted for
some of the discrepancies. It is clear
that there has been confusion over
the region included (where), types
of wetland and/or upland included
in the estimates (what) and the
timeframe of when losses occurred
(when). This study measured
changes in marine and estuarine
wetlands from 1998 to 2004 as
described earlier.
One or more of several interrelated
factors may have contributed to
the loss of estuarine emergent
wetland, including: deficiencies in
sediment deposition, canals and
artificially created waterways,
wave erosion, land subsidence, and
salt water intrusion causing marsh
disintegration. In recognizing that
human activities have affected
wetlands in Louisiana, Williams et
al. (1995) cited an extensive system
of dredged canals and flood-control
structures constructed to facilitate
hydrocarbon exploration and
production as well as commercial
and recreational boat traffic that had
enabled salt water to intrude from
the Gulf of Mexico as major factors
in wetland loss.
Coastal storms often have had a
role in destabilizing salt marsh
substrates by washing away
sediment with wind driven
floodwaters (Chabreck 1988).
Estimates of estuarine emergent
area reported here, were made
prior to Hurricane Katrina and Rita
during the summer of 2005. These
storm events may have further
exacerbated vegetated marsh losses
by creating open water pockets or
lakes to replace vegetated wetlands
in St. Bernard and Plaquemines
Parishes, Louisiana (USGS 2005b).
Estuarine emergent wetlands have
been restored elsewhere in the
country. An estimated 2,540 acres
were reclaimed from freshwater
wetlands through projects such as
the Dande Meadows Salt Marsh
Project in Massachusetts. This
project restored natural salt marsh
that had been converted into a
freshwater hayfield during colonial
times (Coastal America 2003). Small
to moderate scale projects have
been undertaken within the National
Estuarine Research Reserve System
as well. There, the focus has been on
restoring salt marsh and seagrass
beds where ecological functions have
declined (Kennish 2004).
Table 4. Contrasting different estimates of wetland loss in Louisiana.
Habitat Description Estimated Loss Rate
Normalized1 Loss
Rate (Hectares per
Year)
Source
Coastal marsh 50 acres/day 7,390 ha Moorman (2005)
Ducks Unlimited Southern Region
Coast and wetlands 25 sq. mi./yr 6,480 ha Louisiana State University (2005)
Wetlands of coastal
Louisiana
50 sq. mi./yr 12,960 ha Louisiana Geological Survey and EPA (1987)
Louisiana’s wetlands 75 sq. km/yr 7,500 ha Williams (1995)
USGS—Marine and Coastal Geology Program
Louisiana’s wetlands 16,000 to 25,000 acres/yr 6,480 to 10,120 ha National Marine Fisheries Service (www.nmfs.noaa.
gov/habitat)(2005)
Coastal land 25 to 35 sq. mi/yr 6,480 to 9,070 ha Tulane University (2004)
Marsh 40 sq. mi./yr 10,360 ha USGS, National Wetland Research Center (2005)
Estuarine and Marine
emergent wetland
5,500 acres/yr 2,240 ha This Study
1Scaled to 365 days and expressed as hectares.
Conversion factors:
Square mile = 640 acres
Hectare = 2.47 acres
Square kilometer = 247 acres
54
Estuarine Shrub
Wetlands
Among the most notable components
of the estuarine shrub wetland
category are mangrove swamps.
The geographic extent of mangroves
has been influenced by cold
temperatures, hurricanes, and
human induced stressors (Spalding
et al. 1997). Florida has always been
the primary location of mangrove
wetlands in the United States.
Mangrove species are uniquely
adapted to saline environments
and ecologically mangroves have
supported a diversity of wildlife
(Odum and McIvor 1990). Mangrove
communities and surrounding
waters of south Florida support
more than 220 species of fish, 24
species of reptiles and amphibians,
18 mammals and 181 bird species
(U.S. Fish and Wildlife Service 1996)
(Figure 36).
Mitsch and Gosselink (1993)
indicated that the northern-most
extent of black mangrove (Avicennia
geminans) occurred at about 30
degrees N. latitude. Although
scattered stands of mangrove shrubs
have been found along the north
coast of the Gulf of Mexico (Odum
and McIvor 1990), these wetlands
have been exposed to freezing
temperatures that greatly reduced
their number and distribution.
Estuarine shrub wetlands may have
included woody species other than
mangroves. Other salt-tolerant
or invasive woody plants in these
northern wetlands included false
willow (Baccharis angustifolia),
saltbush (Baccharis halimifolia),
buttonwood (Conocarpus erectus),
bay cedar (Suriana maritina)
and Brazilian pepper (Schinus
terebinthifolius).
There were an estimated 682,200
acres (276,190 ha) of estuarine shrub
wetland in 2004. This estimate
represented a gain of about 800
acres (320 ha). Most of this gain
came from areas formerly classified
as estuarine emergent wetland.
The acreage estimates of estuarine
shrub wetlands have been steady or
increased slightly over the past two
decades.
The long term trend in all intertidal
wetlands, estuarine vegetated and
estuarine non-vegetated categories
is shown in Figure 37 A-C. Estuarine
vegetated wetlands have continued
to decline over time as losses to the
estuarine emergent category have
overshadowed the small gains to
estuarine shrub wetlands.
Figure 36. Pelican Island, Florida, the nation’s first National Wildlife Refuge is located in the Indian River Lagoon, a
biologically diverse estuary of mangrove islands, salt marsh, and maritime hammocks. Photo courtesy of the FWS.
55
Figure37 A–C. Long-term trends in A) all intertidal wetlands, B) estuarine vegetated wetlands and C) estuarine non-vegetated
wetlands, 1950s to 2004.
56
5,000
5,200
5,400
5,600
5,800
6,000
6,200
Acres (in Thousands)
B. Estuarine Vegetated Wetlands
4,200
4,400
4,600
4,800
5,000
5,200
1950s 1970s 1980s 1998 2004
Acres (in Thousands)
C. Estuarine Non-vegetated Wetlands
0
200
400
600
800
1,000
1950s 1970s 1980s 1998 2004
Acres (in Thousands)
A. All Intertidal Wetlands
6,000
5,500
5,399
5,329
5,300
1950s 1970s 1980s 1998 2004
4,604
4,572
4,623
4,854
5,000
594 594 600
678
741
Wetland Values for Fish and Wildlife
Wetlands and Fish
Formed in 1922, The Izaak Walton League is one
of the nation’s oldest conservation organizations
to address deteriorating conditions of America’s top
fishing streams. The League is named for the 17th-century
English angler-conservationist who wrote the
literary classic “The Compleat Angler.” Since 1992,
the League has been restoring wetlands and streams,
establishing wildlife refuges and parks, and teaching
outdoor ethics to outdoor enthusiasts, sportsmen
and conservationists. League members recognize
the importance of wetlands and the role they play
in supporting fish species and angling opportunities
throughout the United States.
Fish and seafood provide the largest source of protein
for people across the world. The worldwide fish harvest
has surpassed cattle production and poultry farming
as the primary source of animal protein (FAO 1987).
The United States consumes more than 4 billion tons of
fish and shellfish every year—an average of 16 pounds
per person (National Marine Fisheries Service 2004).
Additionally, about 34 million people in the United
States fish for recreation (USFWS 2001).
America’s coastal and freshwater fish populations are
currently facing an unprecedented decline. Since 1900,
123 aquatic freshwater species have become extinct
in North America. Of the 822 native freshwater fish
species in the United States, 39 percent are at risk
of extinction (Fisheries and Water Resources Policy
Committee 2004) and 72 percent of freshwater mussels
are imperiled (USFWS 2004a). Additionally, the world’s
catch of ocean fish has been steadily falling since 1989,
with 13 of the 17 most productive fisheries currently
facing steep declines. Several factors have contributed
to this decline, including over-fishing and pollution.
However, the rate at which America’s fish populations
are plummeting is largely due to the loss and alteration
of their aquatic habitats.
At one time, the conterminous United States contained
more than 220 million acres of wetland habitat.
Although government programs, conservation
organizations, and private individuals are slowing
wetland loss and restoring degraded wetlands, the total
wetland acreage in the lower 48 states has declined to
the current 107 million acres. The nation’s wetlands are
vital to fish health. Wetlands provide an essential link
in the life cycle of 75 percent of the fish and shellfish
commercially harvested in the United States, and up
to 90 percent of the recreational fish catch. Wetlands
provide clean water, a consistent food supply, shelter,
and nursery areas for both marine and freshwater
species. Salmon, winter flounder, and largemouth bass,
among others, depend on healthy wetlands.
Largemouth bass (Micropterus salmoides) is the most popular game fish in the
United States. Shallow marshes at the edges of lakes and floodplain wetlands of
large, slow moving rivers are favorite habitats for the largemouth bass. Stocking
largemouth in smaller ponds and recreational lakes has been a common sport
fishery management practice in many states. Image courtesy of FWS.
57
By providing essential habitat and other benefits to fish
populations, wetlands play a crucial role in maintaining
the long-term health of our aquatic resources and
contribute to economic prosperity. Sport fishing is
responsible for a multi-million dollar industry that
supports television shows, magazines, fishing clubs
and organizations, tackle and boat manufacturing and
fishing tournaments held nationwide. In total, wetland-dependent
species make up 71 percent of the commercial
and recreational fisheries, supporting an industry that
contributes $111 billion annually to our national economy
and employs two million people (Fisheries and Water
Resources Policy Committee 2004).
How Wetlands Support Healthy Fish Populations
Clean Water
Wetlands have been termed “nature’s kidneys” because
they filter and purify our streams, rivers and waterways.
Wetlands slow down
moving water, allowing
sediments suspended in
the water to gradually
settle to the ground.
Cattails (Typha spp.)
and other ermergent and
submergent vegetation
help remove dangerous
heavy metals, like
copper and arsenic,
from the water column.
Other pollutants, like
lead, mercury and
pesticides, are trapped
by soil particles and are
gradually broken down
by microbes. Wetland
plants and microorganisms
also filter out and absorb
excess nutrients that
can result from fertilizer
application, manure, and
municipal sewage. When large amounts of nitrogen
and phosphorus enter our waterways, a massive
overgrowth of algae can occur, depleting dissolved
oxygen levels and stressing fish populations. Wetlands
can remove more than half of the phosphorous and 75
percent of the nitrogen out of the incoming water flow
(U.S. Environmental Protection Agency 1993) This
natural filtering ability reduces the negative impacts
of agricultural and municipal run-off, and it lessesns
the need to implement costly technological solutions.
For example, if half of all the existing wetlands were
destroyed, it would cost over $62 billion per year to
upgrade sewage treatment plants to handle all the extra
pollution (Environmental Defense Fund and World
Wildlife Fund 1992) Some types of wetlands are so good
at this filtration function that environmental managers
construct similar artificial wetlands to treat storm water
and wastewater near urban centers.
58
Sockeye salmon (Oncorhynchus nerka) spend their life in open sea, but return
to freshwater streams to spawn. These fish support one of the most important
commercial fisheries on the Pacific coast. Image courtesy of FWS.
Northern Pike (Esox lucius) and Muskellunge (Esox
masquinongy) are found in heavily vegetated wetlands
in the shallow waters along the edges of lakes and
large rivers. These are some of North America’s most
important freshwater game fish species. Image courtesy
of FWS.
Food Production
The diverse conditions found in wetlands allow
many different types of organisms, some with
highly specialized adaptations, to co-exist within a
small area. This wide range of species is supported
by the extraordinary rates of plant productivity
that characterize most wetland habitats. Some fish
species benefit directly by feeding on plant parts,
while other fish eat the small insects and crustaceans
that live on plants. Some fish prefer wetland plant
material that forms the detritus found on the bottom
of aquatic habitats. Wetlands indirectly nourish the
entire aquatic system when this rich organic matter is
washed downstream, where it benefits fish living many
miles away in the open ocean. Menhaden (Brevoortia
tyrannus), for example, rely upon detritus for a full
third of their diet, even though they live far from the
wetlands where it is produced.
Spawning and Nursery Areas
Fish eggs and young fish have different needs. Some fish
live in other habitats as adults and return to wetlands
to lay their eggs. Defenseless and immobile eggs can
be hidden from predators by underwater vegetation.
Wetland plants and detritus provide a surface for some
fish to attach their eggs. When the eggs hatch, the
vegetation becomes both a protective cover and a food
source. Young fish dart into the wetland vegetation to
hide, while the juvenile stages of bay scallops, hard
clams, and some other shellfish cling to salt marsh
vegetation and seagrasses for several weeks before
settling on the bottom. Most shrimp harvested in the
Gulf of Mexico depend on salt marshes for nurseries, yet
this latest study reports that these salt marsh wetlands
continued to decline by over 33,000 acres (13,450 ha)
between 1998 and 2004.
Refuge
Both adult and juvenile fish use wetlands to hide from
predators. Thick plant growth can visually confuse
predators and disguise small fish. Juvenile muskellunge,
northern pike and other and mottled colored fish can
hide by blending in with surrounding aquatic vegetation.
Dense vegetation and shallow water prevent many
pelagic predators from entering coastal marshes and
freshwater wetlands fringing lakes and rivers. Anchovies
(Engraulis mordax), juvenile snook (Centropomus
undecimalis), and juvenile spotted seatrout (Cynoscion
nebulosus) dart into the intertwining root systems of
mangrove wetlands to escape larger predators. The
root systems of trees and shrubs in floodplain wetlands
allow stream banks to hang over the water, providing
protective habitat for Chinook salmon (Oncorhynchus
tshawytscha), cutthroat trout (Oncorhynchus clarki),
and other fish.
Fish also use wetlands to seek refuge from changes in
water level, velocity, or bad weather. Coho salmon rely
on the calmer waters of forested wetlands adjacent to
streams to escape fast currents during winter floods.
Wetland plants help maintain appropriate levels of
oxygen in the water and keep temperatures cool for
aquatic life.
59
Rainbow trout, Onchorhynchus mykiss.
Image courtesy of FWS.
Black Crappie (Pomoxis nigromaculatus) and White Crappie (Pomoxis
annularis) use submerged vegetation and brush as spawning habitats. Image
courtesy of FWS.
Management and conservation for all aquatic resources
are a shared responsibility. Agencies, organizations and
individuals must continue to be involved in wetlands
and fisheries conservation activities to protect these
important resources.
Leah Miller and Suzanne Zanelli, Izaak
Walton League of America
www.iwla.org
Some of the information in this article was taken from the
publication Wetlands and Fish: Catch the Link, produced by
the Izaak Walton League and the National Marine Fisheries
Service. You can download this publication at http://www.
nmfs.noaa.gov/habitat/habitatconservation/publications/
hcpub.htm
6600
Brook trout, Salvelinus fontinalis
Image courtesy of FWS.
Photos courtesy of FWS.
Freshwater
Wetland
Resources
Freshwater, or palustrine, wetlands
included forested wetlands,
freshwater emergents, shrubs, and
freshwater ponds less than 20 acres
(8 ha). Freshwater wetlands have
been known by many common names
such as swamp, bog, fen, marsh,
swale, oxbow and wet meadow.
Ninety five percent of all wetland
area in the conterminous United
States was freshwater. In 2004, there
were an estimated 102.5 million
acres (41.5 million ha) of freshwater
wetlands. Table 5 summarized the
changes in freshwater wetlands
between 1998 and 2004.
Gains and Losses in Freshwater
Wetlands
There have been large shifts
between the freshwater wetland
types and uplands. Most wetland
loss (e.g. drainage, fills) and wetland
creation and restoration that
occurred between 1998 and 2004
involved some type of freshwater
wetland.
All net gains in wetland area took
place in freshwater systems. Overall,
the estimated net gain in freshwater
wetland area between 1998 and 2004
was 220,200 acres (89,140 ha).
Freshwater wetland gains resulted
from wetland restorations and the
creation of numerous freshwater
ponds (Figure 38). The status of
freshwater ponds is discussed later
in this section.
Wetland Restoration—Between
1987 and 1990, programs to restore
wetlands under the 1985 Food
Security Act added about 90,000
acres (36,400 ha) to the nation’s
wetland base (Dahl and Johnson
1991). Between 1986 and 1997, there
was a net gain of wetland from
“other” uplands of about 180,000
acres (72,900 ha) (Dahl, 2000).
During those previous study periods
wetland restoration and creation was
not sufficient to overcome wetland
losses. From 1986 to 1997, there was
a deficit between freshwater wetland
losses and gains of about 630,000
acres (255,100 ha). This was due to
freshwater wetland conversion to
upland land uses (Dahl 2000).
The federal government works
cooperatively with landowners,
states, tribes and communities
through a number of programs to
achieve restoration, protection and
improvement (see Appendix D). One
of the primary wetland restoration
programs of the Fish and Wildlife
Service is the Partners for Fish and
Wildlife Program. This program has
been available to private landowners
and has provided both technical
and financial assistance to restore
wetlands and other fish and wildlife
habitats. Examples of restoration
projects include restoring wetlands,
planting native trees and grasses,
removal of exotics, prescribed
burning, reconstruction of stream
habitat and reestablishment of fish
passageways (www.fws.gov/partners
2005).
Another restoration program of
the Fish and Wildlife Service is
the North American Waterfowl
Management Plan (NAWMP),
a public-private approach to
managing waterfowl populations.
Cooperation and coordination with
partners and stakeholders is key
to implementation of NAWMP
Table 5 Changes in freshwater wetland area between 1998 and 2004. The coefficient of variation (CV) for each entry
(expressed as a percentage) is given in parentheses.
Area, in Thousands of Acres
Freshwater Wetland Category Estimated Area,
1998
Estimated Area,
2004
Change,
1998–2004
Change
(in Percent)
Freshwater Emergent 26,289.6
(8.0)
26, 147.0
(8.0)
–142.6
*
–0.5
Freshwater Forested 51,483.1
(2.8)
52,031.4
(2.8)
548.2
(56.1)
1.1
Freshwater Shrub 18,542.2
(4.1)
17.641.4
(4.3)
–900.8
(34.2)
–4.9
Freshwater Vegetated Wetlands 96,314.9
(3.0)
95,819.8
(3.0)
–495.1
(35.0)
–0.5
Ponds1 5,534.3
(3.7)
6,229.6
(3.5)
695.4
(13.1)
12.6
Miscellaneous Types2 384.4
(16.3)
404.3
(15.6)
19.9
(54.2)
5.2
Freshwater Non-Vegetated 5,918.7
(3.7)
6,633.9
(3.5)
715.3
(12.8)
12.1
All Freshwater Wetlands 102,233.6
(2.9)
102,453.7
(2.8)
220.2
(77.3)
0.2
* Statistically unreliable.
1Includes the categories: Palustrine Aquatic Bed and Palustrine Unconsolidated Bottom.
2Palustrine Unconsolidated Shore.
Percent coefficient of variation was expressed as (standard deviation/mean) x (100).
61
Figure 38. Approximate density and distribution of freshwater wetland gains identified in the samples of this study.
Figure 39. A tile drained wetland basin has been restored. Ohio, 2005.
62
Wetland Gain
0–50 Acres
51–100 Acres
101–250 Acres
251–600 Acres
Figure 40. Wetland
restoration (freshwater
emergent) on land
previously classified as
upland “other.” Indiana,
2005. Photo by
M. Bergeson.
and to successfully protect and
conserve waterfowl through
habitat protection, restoration,
and enhancement. The habitat
objectives of NAWMP identify
key waterfowl habitat areas and
call for their conservation and
protection. Working with partners
and cooperators NAWMP seeks
to enhance, protect and restore
wetlands that contribute to those
waterfowl habitat objectives.
Over the past decade, many agencies
and organizations have been actively
involved in wetland restoration,
enhancement or creation. Many
beneficial projects have been
completed by federal, state, local
and private organizations and
citizens. Some of these projects
have involved removal of invasive
species in wetlands, restoration
of hydrology to partially drained
habitats, selective plantings and
reestablishment of vegetation,
improved wetland quality and other
habitat improvement activities.
These wetland enhancement
projects have not contributed area
gains to the wetland base and were
not part of this study.
An estimated 564,300 acres (228,460
ha) of wetlands were restored on
agricultural lands between 1998
and 2004. However, the loss of
wetlands to agricultural land use
was responsible for an estimated
488,200 acres (197,650 ha) during the
same period. The net gain of about
76,100 acres ( 30,800 ha) did not tell
the entire story of wetland restored
or created from agricultural
land. As lands became enrolled
in retirement or conservation
programs, they were subsequently
re-classified to the upland “other”
land use category (e.g. there were no
identifiable land use characteristics).
Thus, some areas attributed to
wetland restoration were actually
conversions of upland agricultural
land to the upland “other” category.
Replacement of wetland with a
structure (house or office building)
or development resulting from urban
or suburban infrastructure (roads
and bridges), usually constituted
an irreversible loss (Ainslie 2002).
It follows that most restoration and
creation of freshwater wetlands
would have to come from the
agricultural sector or undeveloped
lands classified as “other.” The
“other” lands category also included
many conservation lands such
as undeveloped land on National
Wildlife Refuges, in state game
management areas or preserves,
idle lands or land in retirement
programs planted to permanent
cover, as well as national and state
park lands (Figure 40). This trend
of gaining wetland acres from the
“other” land use category was seen
in the previous era study where
180,000 acres (72,900 ha) of “other”
land was converted to wetland (Dahl
2000).
63
The Council on Environmental
Quality (2005) provided an
assessment of wetland restoration
and creation by federal programs
that showed 58 percent of
the acreage was attributed to
agricultural conservation and
technical assistance programs and
about 32 percent was attributed
to other federal initiatives such as
those completed on conservation
lands.
The National Resources Inventory
conducted by the U.S. Department
of Agriculture estimated a total net
change of 263,000 acres (106,470
ha) in freshwater and estuarine
wetlands on nonfederal land from
Figure 41. Wetland restoration attributed to agricultural conservation programs in the upper midwest, 2004. The wetland can be
seen in the center with light green and white vegetation, darker irregular shape is surface water with vegetation.
1997 to 2003 (USDA—NRCS 2004).
Despite subtle differences and
nuances between that study and
this study and different timeframes,
there was general agreement
between the studies with regard to
wetland trends due to agriculture.
Agricultural conservation programs